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Theoretical Study of the Inverting Mechanism in a Processive Cellobiohydrolase with Quantum Mechanical Calculations
Kim, S.; Payne, C. M.; Himmel, M. E.; Crowley, M. F.; Paton, R. S.; Beckham, G. T.
The Hypocrea jecorina Family 6 cellobiohydrolase (Cel6A) is one of most efficient enzymes for cellulose deconstruction to soluble sugars and is thus of significant current interest for the growing biofuels industry. Cel6A is known to hydrolyze b(1,4)-glycosidic linkages in cellulose via an inverting mechanism, but there are still questions that remain regarding the role of water and the catalytic base. Here we study the inverting, single displacement, hydrolytic reaction mechanism in Cel6A using density functional theory (DFT) calculations. The computational model used to follow the reaction is a truncated active site model with several explicit waters based on structural studies of H. jecorina Cel6A. Proposed mechanisms are evaluated with several density functionals. From our calculations, the role of the water in nucleophilic attack on the anomeric carbon, and the roles of several residues in the active site loops are elucidated explicitly for the first time. We also apply quantum mechanical calculations to understand the proton transfer reaction which completes the catalytic cycle.
The molecular recognition of ?-cyclodextrin modified CdSe quantum dots with tyrosine enantiomers: Theoretical calculation and experimental study
NASA Astrophysics Data System (ADS)
Cao, Yujuan; Wu, Shuangshuang; Liang, Yaozhen; Yu, Ying
In the present work, the molecular recognition of mono-(6-mercapto)-?-cyclodextrin modified CdSe quantum dots (?-CD/CdSe QDs) with tyrosine enantiomers were investigated with theoretical calculation and fluorescence spectroscopy. The inclusion processes and the most probable structures of the inclusion complexes were simulated using PM3 energy scanning and optimization method. The trends of stability of the two inclusion complexes deduced from their calculated stabilization energies were studied. Moreover, the fluorescence spectra of ?-CD/CdSe QDs in the presence of tyrosine enantiomers as well as the effect of ionic strength on the complexation of ?-CD/CdSe QDs-tyrosine were discussed. The experimental results indicated that the ?-CD/CdSe QDs have better enantioselectivity to L-tyrosine than that to D-tyrosine, and good linearity between the fluorescence intensity of ?-CD/CdSe QDs and L-tyrosine over the concentration range from 0.10 ū 10-4 mol/L to 4.00 ū 10-4 mol/L with relative coefficient of 0.9909 was obtained. The experimental data agrees well with that obtained from theoretical calculation, indicating that ?-cyclodextrin modified CdSe quantum dots contained good inclusion capability and fluorescence property, it has good potential application in the field of biological diagnosis, analysis, etc.
Theoretical investigation of photonic quantum wells and defects
Yuankai Jiang
In this dissertation, band gaps of photonic crystal slabs are calculated and single and multiple photonic quantum well systems are theoretically investigated. A comprehensive study of defects in the photonic crystal is also presented in the dissertation. The major milestones and current developments in the photonic crystal research are briefly outlined in the introduction. Four theoretical approaches most commonly applied
Theoretical modeling of large molecular systems. Advances in the local self consistent field method for mixed quantum mechanics/molecular mechanics calculations.
Monari, Antonio; Rivail, Jean-Louis; Assfeld, Xavier
Molecular mechanics methods can efficiently compute the macroscopic properties of a large molecular system but cannot represent the electronic changes that occur during a chemical reaction or an electronic transition. Quantum mechanical methods can accurately simulate these processes, but they require considerably greater computational resources. Because electronic changes typically occur in a limited part of the system, such as the solute in a molecular solution or the substrate within the active site of enzymatic reactions, researchers can limit the quantum computation to this part of the system. Researchers take into account the influence of the surroundings by embedding this quantum computation into a calculation of the whole system described at the molecular mechanical level, a strategy known as the mixed quantum mechanics/molecular mechanics (QM/MM) approach. The accuracy of this embedding varies according to the types of interactions included, whether they are purely mechanical or classically electrostatic. This embedding can also introduce the induced polarization of the surroundings. The difficulty in QM/MM calculations comes from the splitting of the system into two parts, which requires severing the chemical bonds that link the quantum mechanical subsystem to the classical subsystem. Typically, researchers replace the quantoclassical atoms, those at the boundary between the subsystems, with a monovalent link atom. For example, researchers might add a hydrogen atom when a C-C bond is cut. This Account describes another approach, the Local Self Consistent Field (LSCF), which was developed in our laboratory. LSCF links the quantum mechanical portion of the molecule to the classical portion using a strictly localized bond orbital extracted from a small model molecule for each bond. In this scenario, the quantoclassical atom has an apparent nuclear charge of +1. To achieve correct bond lengths and force constants, we must take into account the inner shell of the atom: for an sp(3) carbon atom, we consider the two core 1s electrons and treat that carbon as an atom with three electrons. This results in an LSCF+3 model. Similarly, a nitrogen atom with a lone pair of electrons available for conjugation is treated as an atom with five electrons (LSCF+5). This approach is particularly well suited to splitting peptide bonds and other bonds that include carbon or nitrogen atoms. To embed the induced polarization within the calculation, researchers must use a polarizable force field. However, because the parameters of the usual force fields include an average of the induction effects, researchers typically can obtain satisfactory results without explicitly introducing the polarization. When considering electronic transitions, researchers must take into account the changes in the electronic polarization. One approach is to simulate the electronic cloud of the surroundings by a continuum whose dielectric constant is equal to the square of the refractive index. This Electronic Response of the Surroundings (ERS) methodology allows researchers to model the changes in induced polarization easily. We illustrate this approach by modeling the electronic absorption of tryptophan in human serum albumin (HSA). PMID:23249409
Group theoretical quantum tomography G. Cassinellia)
D'Ariano, Giacomo Mauro
Group theoretical quantum tomography G. Cassinellia) Dipartimento di Fisica, Universita` di Genova foundation of quantum tomography using the theory of square-integrable representations of unimodular Lie) can be computed in terms of Tr (QnT). In order to implement this scheme one has to estimate Tr (Qn
Quantum transport calculations using periodic boundaryconditions
Wang, Lin-Wang
An efficient new method is presented to calculate the quantum transports using periodic boundary conditions. This method allows the use of conventional ground state ab initio programs without big changes. The computational effort is only a few times of a normal groundstate calculations, thus is makes accurate quantum transport calculations for large systems possible.
Information-theoretic limits to quantum cryptography
NASA Astrophysics Data System (ADS)
Barnett, Stephen M.; Phoenix, Simon J. D.
We develop an information-theoretic formalism to describe a quantum-cryptographically protected communication channel. We thereby establish the fundamental limits on the security of the channel. This formalism enables us to propose protocols that allow detection of an eavesdropper by examination of data that would normally be discarded.
Theoretical Chemistry I Quantum Mechanics 16 October 2008
Pfeifer, Holger
Theoretical Chemistry I Quantum Mechanics Axel Gro▀ 16 October 2008 #12;#12;Preface Theoretical Chemistry 1 Quantum Mechanics Prof. Dr. Axel Gro▀ Phone: 50Ł22819 Room No.: O25/342 Email: axel of Quantum Mechanics 3. Quantum Dynamics 4. Angular Momentum 5. Approximation Methods 6. Symmetry in Quantum
Calculations of theoretical strength: State of the art and history
J. Pokluda; M. ?ern²; P. Ŗandera; M. Ŗob
Current state and historical evolution of theoretical strength calculations is presented as a brief overview completed by a database of selected theoretical and experimental results. Principles of a sophisticated analysis of mechanical stability of crystals are elucidated by means of a schematic example. Stability conditions and Jacobian matrixes are presented for selected crystalline symmetries and deformation paths. The importance of
Theoretical calculations of He scattering intensities from MgO
Schwartz, C.; Karimi, M.; Vidali, G.
We report close-coupling calculations of the specular intensity of He atoms scattered from the (100) surface of MgO. The atom-surface interactions used in this study were developed within a semiempirical effective-medium theory. We find good agreement between the experimentally determined and theoretically calculated specular scattering intensities. We further identify features in the theoretical spectra that are sensitive to the size of the Fourier components, which can be used to refine further the input potentials.
Calculating unknown eigenvalues with a quantum algorithm
NASA Astrophysics Data System (ADS)
Zhou, Xiao-Qi; Kalasuwan, Pruet; Ralph, Timothy C.; O'Brien, Jeremy L.
A quantum algorithm solves computational tasks using fewer physical resources than the best-known classical algorithm. Of most interest are those for which an exponential reduction is achieved. The key example is the phase estimation algorithm, which provides the quantum speedup in Shor's factoring algorithm and quantum simulation algorithms. To date, fully quantum experiments of this type have demonstrated only the read-out stage of quantum algorithms, but not the steps in which input data is read in and processed to calculate the final quantum state. Indeed, knowing the answer beforehand was essential. We present a photonic demonstration of a full quantum algorithm--the iterative phase estimation algorithm (IPEA)--without knowing the answer in advance. This result suggests practical applications of the phase estimation algorithm, including quantum simulations and quantum metrology in the near term, and factoring in the long term.
Photophysical study and theoretical calculations of an ionic liquid crystal bearing oxadiazole
NASA Astrophysics Data System (ADS)
Pedro, Jorge A.; Mora, Josķ R.; Westphal, Eduard; Gallardo, Hugo; Fiedler, Haidi D.; Nome, Faruk
We report a detailed photophysical study of 1-dodecyl-4-[5-(4-dodecyloxyphenyl)-1,3,4-oxadiazole-2-yl]pyridinium bromide (454Do), a cationic amphiphile that behaves as a fluorescent liquid crystal. Excitation and emission spectra of the probe in different environments result in significant changes in quantum yields which are correlated with changes in lifetimes and theoretical calculations.
Quantum Monte Carlo Calculations of Light Nuclei
Steven C. Pieper
During the last 15 years, there has been much progress in defining the nuclear Hamiltonian and applying quantum Monte Carlo methods to the calculation of light nuclei. I describe both aspects of this work and some recent results.
Linear-scaling quantum Monte Carlo calculations.
Williamson, A J; Hood, R Q; Grossman, J C
A method is presented for using truncated, maximally localized Wannier functions to introduce sparsity into the Slater determinant part of the trial wave function in quantum Monte Carlo calculations. When combined with an efficient numerical evaluation of these localized orbitals, the dominant cost in the calculation, namely, the evaluation of the Slater determinant, scales linearly with system size. This technique is applied to accurate total energy calculation of hydrogenated silicon clusters and carbon fullerenes containing 20-1000 valence electrons. PMID:11736525
Multi-million atom electronic structure calculations for quantum dots
NASA Astrophysics Data System (ADS)
Usman, Muhammad
Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In the past decade or so, these nanostructures have attracted significant experimental and theoretical attention in the field of nanoscience. The new and tunable optical and electrical properties of these artificial atoms have been proposed in a variety of different fields, for example in communication and computing systems, medical and quantum computing applications. Predictive and quantitative modeling and simulation of these structures can help to narrow down the vast design space to a range that is experimentally affordable and move this part of nanoscience to nano-Technology. Modeling of such quantum dots pose a formidable challenge to theoretical physicists because: (1) Strain originating from the lattice mismatch of the materials penetrates deep inside the buffer surrounding the quantum dots and require large scale (multi-million atom) simulations to correctly capture its effect on the electronic structure, (2) The interface roughness, the alloy randomness, and the atomistic granularity require the calculation of electronic structure at the atomistic scale. Most of the current or past theoretical calculations are based on continuum approach such as effective mass approximation or k.p modeling capturing either no or one of the above mentioned effects, thus missing some of the essential physics. The Objectives of this thesis are: (1) to model and simulate the experimental quantum dot topologies at the atomistic scale; (2) to theoretically explore the essential physics i.e. long range strain, linear and quadratic piezoelectricity, interband optical transition strengths, quantum confined stark shift, coherent coupling of electronic states in a quantum dot molecule etc.; (3) to assess the potential use of the quantum dots in real device implementation and to provide physical insight to the experimentalists. Full three dimensional strain and electronic structure simulations of quantum dot structures containing multi-million atoms are done using NEMO 3-D. Both single and vertically stacked quantum dot structures are analyzed in detail. The results show that the strain and the piezoelectricity significantly impact the electronic structure of these devices. This work shows that the InAs quantum dots when placed in the InGaAs quantum well red shifts the emission wavelength. Such InAs/GaAs-based optical devices can be used for optical-fiber based communication systems at longer wavelengths (1.3um -- 1.5um). Our atomistic simulations of InAs/InGaAs/GaAs quantum dots quantitatively match with the experiment and give the critical insight of the physics involved in these structures. A single quantum dot molecule is studied for coherent quantum coupling of electronic states under the influence of static electric field applied in the growth direction. Such nanostructures can be used in the implementation of quantum information technologies. A close quantitative match with the experimental optical measurements allowed us to get a physical insight into the complex physics of quantum tunnel couplings of electronic states as the device operation switches between atomic and molecular regimes. Another important aspect is to design the quantum dots for a desired isotropic polarization of the optical emissions. Both single and coupled quantum dots are studied for TE/TM ratio engineering. The atomistic study provides a detailed physical analysis of these computationally expensive large nanostructures and serves as a guide for the experimentalists for the design of the polarization independent devices for the optical communication systems.
Information-theoretic postulates for quantum theory
Markus P. Mueller; Lluis Masanes
Why are the laws of physics formulated in terms of complex Hilbert spaces? Are there natural and consistent modifications of quantum theory that could be tested experimentally? This book chapter gives a self-contained and accessible summary of our paper [New J. Phys. 13, 063001, 2011] addressing these questions, presenting the main ideas, but dropping many technical details. We show that the formalism of quantum theory can be reconstructed from four natural postulates, which do not refer to the mathematical formalism, but only to the information-theoretic content of the physical theory. Our starting point is to assume that there exist physical events (such as measurement outcomes) that happen probabilistically, yielding the mathematical framework of "convex state spaces". Then, quantum theory can be reconstructed by assuming that (i) global states are determined by correlations between local measurements, (ii) systems that carry the same amount of information have equivalent state spaces, (iii) reversible time evolution can map every pure state to every other, and (iv) positivity of probabilities is the only restriction on the possible measurements.
Theoretical gain of [hhk]-oriented quantum wire lasers
NASA Astrophysics Data System (ADS)
Yamaguchi, A. Atsushi; Usui, Akira
Optical gain in quantum wire (QWI) lasers are theoretically investigated as functions of wire crystallographic direction taking valence band anisotropy into account. Calculations for GaAs cylindrical QWI with infinite barriers are performed by using the 4ū4 Luttinger-Kohn Hamiltonian. Considering the structural optimization of QWI lasers from the viewpoint of crystallographic direction, we find that a [111]-QWI lasers is the most suitable low-threshold laser and that a [1,-1,0]-QWI laser on a (110) substrate is the most suitable polarization-stab-ilized vertical-cavity surface-emitting laser.
A quantum theoretical study of polyimides
NASA Technical Reports Server (NTRS)
Burke, Luke A.
One of the most important contributions of theoretical chemistry is the correct prediction of properties of materials before any costly experimental work begins. This is especially true in the field of electrically conducting polymers. Development of the Valence Effective Hamiltonian (VEH) technique for the calculation of the band structure of polymers was initiated. The necessary VEH potentials were developed for the sulfur and oxygen atoms within the particular molecular environments and the explanation explored for the success of this approximate method in predicting the optical properties of conducting polymers.
Quantum Theoretical Study of KCl and LiCl Clusters
NASA Astrophysics Data System (ADS)
Koetter, Ted; Hira, Ajit; Salazar, Justin; Jaramillo, Danelle
This research focuses on the theoretical study of molecular clusters to examine the chemical properties of small KnClnandLinCln clusters (n = 2 - 20). The potentially important role of these molecular species in biochemical and medicinal processes is well known. This work applies the hybrid ab initio methods of quantum chemistry to derive the different alkali-halide (MnHn) geometries. Of particular interest is the competition between hexagonal ring geometries and rock salt structures. Electronic energies, rotational constants, dipole moments, and vibrational frequencies for these geometries are calculated. Magic numbers for cluster stability are identified and are related to the property of cluster compactness. Mapping of the singlet, triplet, and quintet, potential energy surfaces is performed. Calculations were performed to examine the interactions of these clusters with some atoms and molecules of biological interest, including O, O2, and Fe. Potential design of new medicinal drugs is explored.
Calculating the social cost of illegal drugs: a theoretical approach.
Diomidous, Marianna; Zimeras, Stelios; Mechili, Aggelos
The use of illegal drugs generates a wide range of social harms depending on various ways, according to the policy definition of the problem. The challenge is the way to model the impact of illegal drugs use during a long time period considering the factors that affects the process. Based on these models, estimation could be measured and prediction could be achieved. The illegal drugs use might affect the economic and social structure of the public system leading to direct and effective decisions to overcome the problematic. For that reason, calculation of social cost related to the use of illegal could be introduced over time (t) as a proposed social measure to define the variability of social indicator on society. In this work, a theoretical approach for the calculation of social cost of illegal drugs is proposed and models over time are defined. PMID:23823436
Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system
Edgar A. Gomez; J. D. Hernandez-Rivero; Herbert Vinck-Posada
We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems. In particular, we investigate the potential of this theoretical approach by its application to compute the emission spectrum of a dissipative system composed by a single quantum dot inside of a semiconductor cavity. We also describe a simple algorithm based on the Green's functions technique for calculating the emission spectrum of the quantum dot as well as of the cavity which can easily be implemented in any numerical linear algebra package. We find that the Green's functions technique demonstrates a better accuracy and efficiency in the calculation of the emission spectrum and it allows to overcome the inherent theoretical difficulties associated to the direct application of the quantum regression theorem approach.
Preliminary theoretical acoustic and rf sounding calculations for MILL RACE
Warshaw, S.I.; Dubois, P.F.
As participant in DOE/ISA's Ionospheric Monitoring Program, LLNL has the responsibility of providing theoretical understanding and calculational support for experimental activities carried out by Los Alamos National Laboratory in using ionospheric sounders to remotely detect violent atmospheric phenomena. We have developed a system of interconnected computer codes which simulate the entire range of atmospheric and ionospheric processes involved in this remote detection procedure. We are able to model the acoustic pulse shape from an atmospheric explosion, the subsequent nonlinear transport of this energy to all parts of the immediate atmosphere including the ionosphere, and the propagation of high-frequency ratio waves through the acoustically perturbed ionosphere. Los Alamos' coverage of DNA's MILL RACE event provided an excellent opportunity to assess the credibility of the calculational system to correctly predict how ionospheric sounders would respond to a surface-based chemical explosion. In this experiment, 600 tons of high explosive were detonated at White Sands Missile Range at 12:35:40 local time on 16 September 1981. Vertical incidence rf phase sounders and bistatic oblique incidence rf sounders fielded by Los Alamos and SRI International throughout New Mexico and southern Colorado detected the ionospheric perturbation that ensued. A brief account of preliminary calculations of the acoustic disturbance and the predicted ionospheric sounder signatures for MILL RACE is presented. (WHK)
Quantum Hardcore Functions by Complexity-Theoretical Quantum List Decoding
Akinori Kawachi; Tomoyuki Yamakami
Hardcore functions have been used as a technical tool to construct secure cryptographic systems; how- ever, little is known on their quantum counterpart, called quantum hardcore functions. With a new in- sight into fundamental properties of quantum hardcores, we present three new quantum hardcore functions for any (strong) quantum one-way function. We also give a \\
Collected Calculations in Quantum Gravity and QED
NASA Astrophysics Data System (ADS)
Sawhill, Bruce Kean
In the first part of this thesis, I present a calculation of the helicity amplitudes of electron-positron double bremsstrahlung in the massless limit. Using a representation for free photon polarizations developed by a group of European physicists, helicity amplitudes for double bremsstrahlung in the massless limit are calculated for all possible combinations of helicities in the two incoming and four outgoing particle states. The calculation is made possible by the vast simplification which occurs at the amplitude level because of the gauge cancellations caused by expressing the photon polarizations in terms of the fermion momenta to which they are attached. The results of the calculation are discussed in terms of possible use as a polarization monitor for future generations of colliding beam machines in which the beams could be polarized. It is found that, although the total cross-section is easily measured experimentally, the polarization asymmetry is very difficult to measure unless the flux is very high. The possibility of using double bremsstrahlung as a means of analyzing the zed-zero is discussed. The applications for this purpose are very promising, as the shape and amplitude of the cross-section are very dependent on the chiral structure of the mediating particle. In the second part of this work, I present a calculation of the cosmological constant to two loops in matterless quantum gravity. A quantization method originally developed by 't Hooft and Veltman and later modified by M. Mueller is used. This is the standard path integral formulation of gravity modified such that it takes into account the dependence of the action functional on the fluctuating metric, an effect which is normally discarded because dimensional regularization nullifies its contributions. The purpose of the calculation was to explore more fully an intriguing result found by Mark Mueller while performing the same calculation to one-loop order; namely, the quantum corrections to the cosmological constant were identically zero independent of the regularization scheme used regulate the loop integrals, as the coefficients of these integrals identically cancelled for any number of space-time dimensions. In performing the two-loop calculation it was found that the one-loop result no longer holds, and that a regularization scheme must be specified. The possibility of using higher-derivative couplings in gravity is discussed as a means of cutting off the loop-momentum integrals.
Quantum mechanical calculations to chemical accuracy
NASA Technical Reports Server (NTRS)
Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.
The accuracy of current molecular-structure calculations is illustrated with examples of quantum mechanical solutions for chemical problems. Two approaches are considered: (1) the coupled-cluster singles and doubles (CCSD) with a perturbational estimate of the contribution of connected triple excitations, or CCDS(T); and (2) the multireference configuration-interaction (MRCI) approach to the correlation problem. The MRCI approach gains greater applicability by means of size-extensive modifications such as the averaged-coupled pair functional approach. The examples of solutions to chemical problems include those for C-H bond energies, the vibrational frequencies of O3, identifying the ground state of Al2 and Si2, and the Lewis-Rayleigh afterglow and the Hermann IR system of N2. Accurate molecular-wave functions can be derived from a combination of basis-set saturation studies and full configuration-interaction calculations.
Calorimetric determinations and theoretical calculations of polymorphs of thalidomide
NASA Astrophysics Data System (ADS)
Lara-Ochoa, F.; Pķrez, G. Espinosa; Mijangos-Santiago, F.
The analysis of the thermograms of thalidomide obtained for the two reported polymorphs ? and ? by differential scanning calorimetry (DSC) shows some inconsistencies that are discussed in the present work. The conception of a new polymorph form, named ? ?, allowed us to explain the observed thermal behavior more satisfactorily. This new polymorph shows enantiotropy with both ? and ? polymorphs, reflected in the unique endotherm obtained in the DSC-thermograms, when a heating rate of 10 ░C/min is applied. Several additional experiments, such as re-melting of both polymorph forms, showed that there is indeed a new polymorph with an endotherm located between the endotherms of ? and ?. IR, Raman, and powder X-ray permit us to characterize the isolated compound, resulting from the re-melting of both polymorph forms. Mechanical calculations were performed to elucidate the conformations of each polymorph, and ab initio quantum chemical calculations were performed to determine the energy of the more stable conformers and the spatial cell energy for both polymorphs ? and ?. These results suggested a possible conformation for the newly discovered polymorph ? ?.
NMR Quantum Calculations of the Jones Polynomial
Raimund Marx; Amr Fahmy; Louis Kauffman; Samuel Lomonaco; Andreas Sp÷rl; Nikolas Pomplun; John Myers; Steffen J. Glaser
The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones Polynomial by nuclear-magnetic resonance (NMR), in addition we show how to escape from the limitations of NMR approaches that employ pseudo pure states. Specifically, we use two spin 1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the Trefoil Knot, the Figure Eight Knot and the Borromean Rings. After measuring the state of the molecule in each case, we are able to estimate the value of the Jones Polynomial for each of the knots.
Quantum Hardcore Functions by Complexity-Theoretical Quantum List Decoding
Kawachi, A; Kawachi, Akinori; Yamakami, Tomoyuki
We present three new quantum hardcore functions for any quantum one-way function. We also give a "quantum" solution to Damgard's question (CRYPTO'88) on his pseudorandom generator by proving the quantum hardcore property of his generator, which has been unknown to have the classical hardcore property. Our technical tool is quantum list-decoding of "classical" error-correcting codes (rather than "quantum" error-correcting codes), which is defined on the platform of computational complexity theory and cryptography (rather than information theory). In particular, we give a simple but powerful criterion that makes a polynomial-time computable code (seen as a function) a quantum hardcore for any quantum one-way function. On their own interest, we also give quantum list-decoding algorithms for codes whose associated quantum states (called codeword states) are "almost" orthogonal using the technique of pretty good measurement.
Theoretical calculation of oxygen isotope fractionation factors in carbonate systems
NASA Astrophysics Data System (ADS)
Chacko, Thomas; Deines, Peter
Using established methods of statistical mechanical calculation and a recent compilation of vibrational frequency data, we have computed oxygen isotope reduced partition function ratios ( ? values) for a large number of carbonate minerals. The oxygen isotope ? values of carbonates are inversely correlated to both the mass and radius of the cation bonded to the carbonate anion but neither correlation is good enough to be used as a precise and accurate predictor of ? values. There is an approximately 0.6% relative increase in the ? values of aragonite per 10 kbar increase in pressure. These estimates of the pressure effect on ? values are broadly similar to those deduced previously for calcite using the methods of mineral physics. In comparing the ? values of our study with those derived recently from first-principles lattice dynamics calculations, we find near-perfect agreement for calcite and witherite (<0.3% deviation), reasonable agreement for dolomite (<0.9% deviation) and somewhat poorer agreement for aragonite and magnesite (1.5-2% deviation). In the system for which we have the most robust constraints, CO 2-calcite, there is excellent agreement between our calculations and experimental data over a broad range of temperatures (0-900 ░C). Similarly, there is good to excellent correspondence between calculation and experiment for most other low to moderate atomic mass carbonate minerals (aragonite to strontianite). The agreement is not as good for high atomic mass carbonates (witherite, cerussite, otavite). In the case of witherite and cerussite, the discrepancy may be due, in part, to our calculation methodology, which does not account for the effect of cation mass on the magnitude of vibrational frequency shifts associated with heavy isotope substitution. However, the calculations also reveal an incompatibility between the high- and low-temperature experimental datasets for witherite and cerussite. Specifically, the shapes of fractionation factor versus 1/ T2 curves in the calcite-witherite and calcite-cerussite systems do not conform to the robust constraints on the basic shape of these curves provided by theory. This suggests that either the high- or low-temperature datasets for both minerals is in error. Dolomite-calcite fractionation factors derived from our calculations fall within the wide range of fractionations for this system given by previous experimental and natural sample studies. However, our compilation of available low-temperature (25-80 ░C) experimental data reveal an unusual temperature dependence of fractionations in this system; namely, the data indicate an increase in the magnitude of fractionations between dolomite (or proto-dolomite) and calcite with increasing temperature. Such a trend is incompatible with theory, which stipulates that fractionations between carbonate minerals must decrease monotonically with increasing temperature. We propose that the anomalous temperature dependence seen in the low-temperature experimental data reflect changes in the crystallinity and degree of cation ordering of the dolomite phase over this temperature interval and the effect these changes have on the vibrational frequencies of dolomite. Similar effects may be present in natural systems at low-temperature and must be considered in applying experimental or theoretical fractionation data to these systems. In nearly all cases, carbonate mineral-calcite fractionation factors given by the present calculations are in as good or better agreement with experimental data than are fractionations derived from semi-empirical bond strength methods.
Entanglement and electron correlation in quantum chemistry calculations
Kais, Sabre
Entanglement and electron correlation in quantum chemistry calculations Z. HUANG, H. WANG and S; in final form 1 July 2006) ElectronŁelectron correlation in quantum chemistry calculations can be analysed. Thus, entanglement might be used as an alternative measure of electron correlation in quantum chemistry
Entanglement as measure of electronelectron correlation in quantum chemistry calculations
Kais, Sabre
Entanglement as measure of electronŁelectron correlation in quantum chemistry calculations Zhen, United States Received 19 March 2005; in final form 12 July 2005 Abstract In quantum chemistry point and the major approach for quanti- tative electronic structure calculations. In quantum chemistry
Quantum Monte Carlo Calculations Applied to Magnetic Molecules
Larry Engelhardt
We have calculated the equilibrium thermodynamic properties of Heisenberg spin systems using a quantum Monte Carlo (QMC) method. We have used some of these systems as models to describe recently synthesized magnetic molecules, and-upon comparing the results of these calculations with experimental data-have obtained accurate estimates for the basic parameters of these models. We have also performed calculations for other systems that are of more general interest, being relevant both for existing experimental data and for future experiments. Utilizing the concept of importance sampling, these calculations can be carried out in an arbitrarily large quantum Hilbert space, while still avoiding any approximations that would introduce systematic errors. The only errors are statistical in nature, and as such, their magnitudes are accurately estimated during the course of a simulation. Frustrated spin systems present a major challenge to the QMC method, nevertheless, in many instances progress can be made. In this chapter, the field of magnetic molecules is introduced, paying particular attention to the characteristics that distinguish magnetic molecules from other systems that are studied in condensed matter physics. We briefly outline the typical path by which we learn about magnetic molecules, which requires a close relationship between experiments and theoretical calculations. The typical experiments are introduced here, while the theoretical methods are discussed in the next chapter. Each of these theoretical methods has a considerable limitation, also described in Chapter 2, which together serve to motivate the present work. As is shown throughout the later chapters, the present QMC method is often able to provide useful information where other methods fail. In Chapter 3, the use of Monte Carlo methods in statistical physics is reviewed, building up the fundamental ideas that are necessary in order to understand the method that has been used in this work. With these ideas in hand, we then provide a detailed explanation of the current QMC method in Chapter 4. The remainder of the thesis is devoted to presenting specific results: Chapters 5 and 6 contain articles in which this method has been used to answer general questions that are relevant to broad classes of systems. Then, in Chapter 7, we provide an analysis of four different species of magnetic molecules that have recently been synthesized and studied. In all cases, comparisons between QMC calculations and experimental data allow us to distinguish a viable microscopic model and make predictions for future experiments. In Chapter 8, the infamous ''negative sign problem'' is described in detail, and we clearly indicate the limitations on QMC that are imposed by this obstacle. Finally, Chapter 9 contains a summary of the present work and the expected directions for future research.
Quantum Hardcore Functions by Complexity-Theoretical Quantum List Decoding
Akinori Kawachi; Tomoyuki Yamakami
Hardcore functions have been used as a technical tool to construct secure cryptographic systems; however, little is known on their quantum counterpart, called quantum hardcore functions. With a new insight into fundamental properties of quantum hardcores, we present three new quantum hardcore functions for any (strong) quantum one-way function. We also give a "quantum" solution to Damgard's question (CRYPTO'88) on a classical hardcore property of his pseudorandom generator, by proving its quantum hardcore property. Our major technical tool is the new notion of quantum list-decoding of "classical" error-correcting codes (rather than "quantum" error-correcting codes), which is defined on the platform of computational complexity theory and computational cryptography (rather than information theory). In particular, we give a simple but powerful criterion that makes a polynomial-time computable classical block code (seen as a function) a quantum hardcore for all quantum one-way functions. On their own interest, we construct efficient quantum list-decoding algorithms for classical block codes whose associated quantum states (called codeword states) form a nearly phase-orthogonal basis.
A theoretical model of multi-agent quantum computing
NASA Astrophysics Data System (ADS)
Mihelic, F. Matthew
The best design for practical quantum computing is one that emulates the multi-agent quantum logic function of natural biological systems. Such systems are theorized to be based upon a quantum gate formed by a nucleic acid Szilard engine (NASE) that converts Shannon entropy of encountered molecules into useful work of nucleic acid geometric reconfiguration. This theoretical mechanism is logically and thermodynamically reversible in this special case because it is literally constructed out of the (nucleic acid) information necessary for its function, thereby allowing the nucleic acid Szilard engine to function reversibly because, since the information by which it functions exists on both sides of the theoretical mechanism simultaneously, there would be no build-up of information within the theoretical mechanism, and therefore no irreversible thermodynamic energy cost would be necessary to erase information inside the mechanism. This symmetry breaking Szilard engine function is associated with emission and/or absorption of entangled photons that can provide quantum synchronization of other nucleic acid segments within and between cells. In this manner nucleic acids can be considered as a natural model of topological quantum computing in which the nonabelian interaction of genes can be represented within quantum knot/braid theory as anyon crosses determined by entropic loss or gain that leads to changes in nucleic acid covalent bond angles. This naturally occurring biological form of topological quantum computing can serve as a model for workable man-made multi-agent quantum computing systems.
Density functional calculation of the structural and electronic properties of germanium quantum dots
NASA Astrophysics Data System (ADS)
Anas, M. M.; Gopir, G.
We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.
A Universal Operator Theoretic Framework for Quantum Fault Tolerance
Gerald Gilbert; Michael Hamrick; Yaakov S. Weinstein; Vaneet Aggarwal; A. Robert Calderbank
In this paper we introduce a universal operator theoretic framework for quantum fault tolerance. This incorporates a top-down approach that implements a system-level criterion based on specification of the full system dynamics, applied at every level of error correction concatenation. This leads to more accurate determinations of error thresholds than could previously be obtained. This is demonstrated both formally and with an explicit numerical example. The basis for our approach is the Quantum Computer Condition (QCC), an inequality governing the evolution of a quantum computer. We show that all known coding schemes are actually special cases of the QCC. We demonstrate this by introducing a new, operator theoretic form of entanglement assisted quantum error correction, which incorporates as special cases all known error correcting protocols, and is itself a special case of the QCC.
Quantum Molecular Dynamics calculation of electrical and thermal transport properties
NASA Astrophysics Data System (ADS)
Desjarlais, Michael
Dense, strongly-coupled plasmas, with degenerate or partially degenerate electrons--ubiquitous in high energy density physics, inertial fusion, planetary science, and warm dense matter--are very difficult to describe accurately with traditional theoretical approaches. Over the last decade, density functional based molecular dynamics, also know as quantum molecular dynamics (QMD), has emerged as a powerful tool for the study of dense quantum plasmas, providing accurate equation of state, structural, and transport properties. This talk will focus on the QMD calculation of electrical and thermal conductivities with a much higher degree of accuracy than was possible with earlier methods. Within the density functional approach, electrical and thermal conductivities are extracted directly from the electronic orbitals using the Kubo-Greenwood and Chester-Thellung formalisms, circumventing the need to define the ionization states and collision cross sections. These transport calculations have now been used to generate several wide-range transport models for use in large-scale simulation codes, allowing unprecedented simulations of complex experiments. Sandia National Laboratories is a multi program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives
NASA Technical Reports Server (NTRS)
Du, Ping
As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.
Theoretical Calculation and Validation of the Water Vapor Continuum Absorption
NASA Technical Reports Server (NTRS)
Ma, Qiancheng; Tipping, Richard H.
The primary objective of this investigation is the development of an improved parameterization of the water vapor continuum absorption through the refinement and validation of our existing theoretical formalism. The chief advantage of our approach is the self-consistent, first principles, basis of the formalism which allows us to predict the frequency, temperature and pressure dependence of the continuum absorption as well as provide insights into the physical mechanisms responsible for the continuum absorption. Moreover, our approach is such that the calculated continuum absorption can be easily incorporated into satellite retrieval algorithms and climate models. Accurate determination of the water vapor continuum is essential for the next generation of retrieval algorithms which propose to use the combined constraints of multi-spectral measurements such as those under development for EOS data analysis (e.g., retrieval algorithms based on MODIS and AIRS measurements); current Pathfinder activities which seek to use the combined constraints of infrared and microwave (e.g., HIRS and MSU) measurements to improve temperature and water profile retrievals, and field campaigns which seek to reconcile spectrally-resolved and broad-band measurements such as those obtained as part of FIRE. Current widely used continuum treatments have been shown to produce spectrally dependent errors, with the magnitude of the error dependent on temperature and abundance which produces errors with a seasonal and latitude dependence. Translated into flux, current water vapor continuum parameterizations produce flux errors of order 10 W/ml, which compared to the 4 W/m' magnitude of the greenhouse gas forcing and the 1-2 W/m' estimated aerosol forcing is certainly climatologically significant and unacceptably large. While it is possible to tune the empirical formalisms, the paucity of laboratory measurements, especially at temperatures of interest for atmospheric applications, preclude tuning the empirical continuum models over the full spectral range of interest for remote sensing and climate applications. Thus, we propose to further develop and refine our existing far-wing formalism to provide an improved treatment applicable from the near-infrared through the microwave. Based on the results of this investigation, we will provide to the remote sensing/climate modeling community a practical and accurate tabulation of the continuum absorption covering the near-infrared through the microwave region of the spectrum for the range of temperatures and pressures of interest for atmospheric applications.
Theoretical Calculation and Validation of the Water Vapor Continuum Absorption
NASA Technical Reports Server (NTRS)
Ma, Qiancheng; Tipping, Richard H.
The primary objective of this investigation is the development of an improved parameterization of the water vapor continuum absorption through the refinement and validation of our existing theoretical formalism. The chief advantage of our approach is the self-consistent, first principles, basis of the formalism which allows us to predict the frequency, temperature and pressure dependence of the continuum absorption as well as provide insights into the physical mechanisms responsible for the continuum absorption. Moreover, our approach is such that the calculated continuum absorption can be easily incorporated into satellite retrieval algorithms and climate models. Accurate determination of the water vapor continuum is essential for the next generation of retrieval algorithms which propose to use the combined constraints of multispectral measurements such as those under development for EOS data analysis (e.g., retrieval algorithms based on MODIS and AIRS measurements); current Pathfinder activities which seek to use the combined constraints of infrared and microwave (e.g., HIRS and MSU) measurements to improve temperature and water profile retrievals, and field campaigns which seek to reconcile spectrally-resolved and broad-band measurements such as those obtained as part of FIRE. Current widely used continuum treatments have been shown to produce spectrally dependent errors, with the magnitude of the error dependent on temperature and abundance which produces errors with a seasonal and latitude dependence. Translated into flux, current water vapor continuum parameterizations produce flux errors of order 10 W/sq m, which compared to the 4 W/sq m magnitude of the greenhouse gas forcing and the 1-2 W/sq m estimated aerosol forcing is certainly climatologically significant and unacceptably large. While it is possible to tune the empirical formalisms, the paucity of laboratory measurements, especially at temperatures of interest for atmospheric applications, preclude tuning, the empirical continuum models over the full spectral range of interest for remote sensing and climate applications. Thus, we propose to further develop and refine our existing, far-wing formalism to provide an improved treatment applicable from the near-infrared through the microwave. Based on the results of this investigation, we will provide to the remote sensing/climate modeling community a practical and accurate tabulation of the continuum absorption covering the near-infrared through the microwave region of the spectrum for the range of temperatures and pressures of interest for atmospheric applications.
Theoretical method for analyzing quantum dynamics of correlated photons
Koshino, Kazuki; Nakatani, Masatoshi [College of Liberal Arts and Sciences, Tokyo Medical and Dental University, 2-8-30 Konodai, Ichikawa 272-0827 (Japan) and PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012 (Japan)
We present a theoretical method for the efficient analysis of quantum nonlinear dynamics of correlated photons. Since correlated photons can be regarded as a superposition of uncorrelated photons, semiclassical analysis can be applied to this problem. The proposed method is demonstrated for a V-type three-level atom as a nonlinear optical system.
Quantum field theoretical reformulation of the virial theorem
Tadashi Toyoda; Ken-ichi Takiuchi
A rigorous reformulation of the virial theorem for an interacting quantum many-body system with arbitrary spin is presented. The derivation is based on the previously obtained field theoretical canonical generator for the infinitesimal scale transformation of the second quantized Schr÷dinger field [Phys. Rev. A 48 (1993) 3492]. As to spin-dependence of the particle interaction, the new form brings about a
Quantum public-key algorithms to encrypt and authenticate quantum messages with information-theoretic security
Min Liang; Li Yang
Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.
Quantum public-key algorithms to encrypt and authenticate quantum messages with information-theoretic security
Liang, Min
Public-key cryptosystems for quantum messages are considered from two aspects: public-key encryption and public-key authentication. Firstly, we propose a general construction of quantum public-key encryption scheme, and then construct an information-theoretic secure instance. Then, we propose a quantum public-key authentication scheme, which can protect the integrity of quantum messages. This scheme can both encrypt and authenticate quantum messages. It is information-theoretic secure with regard to encryption, and the success probability of tampering decreases exponentially with the security parameter with regard to authentication. Compared with classical public-key cryptosystems, one private-key in our schemes corresponds to an exponential number of public-keys, and every quantum public-key used by the sender is an unknown quantum state to the sender.
Using the Chebychev expansion in quantum transport calculations
NASA Astrophysics Data System (ADS)
Popescu, Bogdan; Rahman, Hasan; Kleinekath÷fer, Ulrich
Irradiation by laser pulses and a fluctuating surrounding liquid environment can, for example, lead to time-dependent effects in the transport through molecular junctions. From the theoretical point of view, time-dependent theories of quantum transport are still challenging. In one of these existing transport theories, the energy-dependent coupling between molecule and leads is decomposed into Lorentzian functions. This trick has successfully been combined with quantum master approaches, hierarchical formalisms, and non-equilibrium Green's functions. The drawback of this approach is, however, its serious limitation to certain forms of the molecule-lead coupling and to higher temperatures. Tian and Chen [J. Chem. Phys. 137, 204114 (2012)] recently employed a Chebychev expansion to circumvent some of these latter problems. Here, we report on a similar approach also based on the Chebychev expansion but leading to a different set of coupled differential equations using the fact that a derivative of a zeroth-order Bessel function can again be given in terms of Bessel functions. Test calculations show the excellent numerical accuracy and stability of the presented formalism. The time span for which this Chebychev expansion scheme is valid without any restrictions on the form of the spectral density or temperature can be determined a priori.
Methods for calculating forces within quantum Monte Carlo simulations.
Badinski, A; Haynes, P D; Trail, J R; Needs, R J
Atomic force calculations within the variational and diffusion quantum Monte Carlo methods are described. The advantages of calculating diffusion quantum Monte Carlo forces with the 'pure' rather than the 'mixed' probability distribution are discussed. An accurate and practical method for calculating forces using the pure distribution is presented and tested for the SiH molecule. The statistics of force estimators are explored and violations of the central limit theorem are found in some cases. PMID:21386380
Theoretical Studies of Pseudomorphic Quantum Well Optoelectronic Devices
John Paul Loehr
I explore the effects of strain on the material and device properties of semiconductor quantum wells, describing the valence band with a 4 x 4 kcdotp Hamiltonian and assuming parabolic conduction bands. Coulombic bound states in the presence of strain, electric fields, and free carriers are calculated nonvariationally for In _{x}Ga_ {1-x}As (on GaAs) and Si_ {1-x}Ge_{x} (on Si) quantum
Anomalous thermal conduction in one dimension: a quantum calculation.
Santhosh, G; Kumar, Deepak
In this paper, we study the thermal conductivity of an anharmonically coupled chain of atoms. Numerical studies using classical dynamics have shown that the conductivity of a chain with nearest neighbor couplings diverges with chain length L as L(alpha); earlier studies found alpha approximately = 0.4 under a range of conditions, but a recent study on longer chains claims alpha = 1/3. Analytically, this problem has been studied by calculating the relaxation rate gamma(q) of the normal modes of vibration as a function of its wave vector q. Two theoretical studies of classical chains, one using the mode-coupling formulation and the other the Boltzmann equation method, led to gamma(q) proportional to q(5/3), which is consistent with alpha = 0.4. Here we study the problem for a quantum anharmonic chain with quartic anisotropy. We develop a low-temperature expansion for gamma(q) and find that, in the regime Dirac's constant omega(q) < k(B)T, gamma(q) is proportional to q(5/3)T2, where omega(q) is the frequency of the mode. In our analysis, the relaxation arises due to umklapp scattering processes. We further evaluate the thermal conductivity of the chain using the Kubo formula, which enables us to take into account the transport relaxation time through vertex corrections for the current-current correlator. This calculation also yields alpha = 0.4. PMID:17930004
Multi channel quantum defect theory calculations of the Rydberg spectra of HCO
NASA Astrophysics Data System (ADS)
Douguet, Nicolas; Orel, Ann
We present a first-principles theoretical study of the photoionization spectra of vibrationally autoionizing Rydberg states converging to excited states of HCO+. The clamped-nuclei scattering matrix, quantum defects parameters and transition dipole moments are explicitly calculated using the complex variational Kohn technique. The multi-channel quantum defect theory and vibrational frame transformation are then used to calculate the absorption spectrum. The results are compared with experimental data on double-resonance spectroscopy of the high Rydberg states of formyl radical. This work is supported by the DOE Office of Basic Energy Science and the National Science Foundation, Grant No's PHY-10-68785 and PHY-11-60611.
Vibrational Spectra of the MLCl{_2} Complex from Theoretical Calculations
NASA Astrophysics Data System (ADS)
Catikkas, Berna
The geometric and vibrational parameters (harmonic and anharmonic frequencies) of the MLCl{_2} [M= Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg; L= Ethylenediamine (en)] donor-acceptor complexes have been studied by using HF and MPW1PW91+iop(3/76=00572004280)/gen methods. Binding, reorganization, atomization, HOMO-LUMO and ionization potential energies have also been calculated with the same method. SQM calculations have been performed by using anharmonic frequencies and experimental data. The obtained results were found to be in good agreement with the corresponding experimental findings.
Theoretical calculation of oxygen isotope fractionation factors in carbonate systems
Thomas Chacko; Peter Deines
Using established methods of statistical mechanical calculation and a recent compilation of vibrational frequency data, we have computed oxygen isotope reduced partition function ratios (? values) for a large number of carbonate minerals. The oxygen isotope ? values of carbonates are inversely correlated to both the mass and radius of the cation bonded to the carbonate anion but neither correlation
A quantum field theoretic description of the delayed choice experiment
R. Srikanth
Wheeler's delayed choice experiment, a well known manifestation of the complementarity principle, has proved somewhat difficult to physically interpret. We show that, restated in quantum field theoretic language, the experiment submits to a simple explanation: that wave- or particle-nature is imposed not at the slit plane but at the detector system. The intepretational difficulty conventionally encountered is due to the assumption of enforcement of complementarity at the former.
Theoretical calculation of zero field splitting parameters of Cr3+ doped ammonium oxalate monohydrate
NASA Astrophysics Data System (ADS)
Kripal, Ram; Yadav, Awadhesh Kumar
Zero field splitting parameters (ZFSPs) D and E of Cr3+ ion doped ammonium oxalate monohydrate (AOM) are calculated with formula using the superposition model. The theoretically calculated ZFSPs for Cr3+ in AOM crystal are compared with the experimental value obtained by electron paramagnetic resonance (EPR). Theoretical ZFSPs are in good agreement with the experimental ones. The energy band positions of optical absorption spectra of Cr3+ in AOM crystal calculated with CFA package are in good match with the experimental values.
Searching for the critical point of QCD: Theoretical benchmark calculations
Lungwitz, Benjamin; Bleicher, Marcus [Institut fuer Kernphysik, Johann Wolfgang Goethe Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main (Germany)
We present a comprehensive study of event-by-event multiplicity fluctuations in nucleon-nucleon and nucleus-nucleus interactions from the BNL Alternating Gradient Synchrotron/GSI Facility for Antiproton and Ion Research to BNL Relativistic Heavy Ion Collider energies within the ultrarelativistic quantum molecular dynamics transport approach. The scaled variances of negative, positive, and all charged hadrons are analyzed. The scaled variance in central Pb+Pb collisions increases with energy and behaves similar to inelastic p+p interactions. We find a nontrivial dependence of multiplicity fluctuations on the rapidity and transverse-momentum interval used for the analysis and on the centrality selection procedure. Quantitative predictions for the NA49 experiment are given, taking into account the acceptance of the detector and the selection procedure of central events.
Potential theoretic methods for far field sound radiation calculations
NASA Technical Reports Server (NTRS)
Hariharan, S. I.; Stenger, Edward J.; Scott, J. R.
In the area of computational acoustics, procedures which accurately predict the far-field sound radiation are much sought after. A systematic development of such procedures are found in a sequence of papers by Atassi. The method presented here is an alternate approach to predicting far field sound based on simple layer potential theoretic methods. The main advantages of this method are: it requires only a simple free space Green's function, it can accommodate arbitrary shapes of Kirchoff surfaces, and is readily extendable to three-dimensional problems. Moreover, the procedure presented here, though tested for unsteady lifting airfoil problems, can easily be adapted to other areas of interest, such as jet noise radiation problems. Results are presented for lifting airfoil problems and comparisons are made with the results reported by Atassi. Direct comparisons are also made for the flat plate case.
Molecular conformational stability and Spectroscopic analysis of Parared with experimental techniques and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Srinivasaraghavan, R.; Thamaraikannan, S.; Seshadri, S.; Gnanasambandan, T.
The complete vibrational assignment and analysis of the fundamental modes of Parared was carried out using the experimental FTIR and FT-Raman data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically from the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of Parared have been computed using B3LYP quantum chemical calculations. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.
Information-theoretic implications of quantum causal structures.
Chaves, Rafael; Majenz, Christian; Gross, David
It is a relatively new insight of classical statistics that empirical data can contain information about causation rather than mere correlation. First algorithms have been proposed that are capable of testing whether a presumed causal relationship is compatible with an observed distribution. However, no systematic method is known for treating such problems in a way that generalizes to quantum systems. Here, we describe a general algorithm for computing information-theoretic constraints on the correlations that can arise from a given causal structure, where we allow for quantum systems as well as classical random variables. The general technique is applied to two relevant cases: first, we show that the principle of information causality appears naturally in our framework and go on to generalize and strengthen it. Second, we derive bounds on the correlations that can occur in a networked architecture, where a set of few-body quantum systems is distributed among some parties. PMID:25562600
Efficient free energy calculations of quantum systems through computer simulations
Alex Antonelli; Rafael Ramirez; Carlos Herrero; Eduardo Hernandez
In general, the classical limit is assumed in computer simulation calculations of free energy. This approximation, however, is not justifiable for a class of systems in which quantum contributions for the free energy cannot be neglected. The inclusion of quantum effects is important for the determination of reliable phase diagrams of these systems. In this work, we present a new
Theoretical calculation of scattering efficiency of isotropic and anisotropic scattering particles employed in nanostructured solar cells
NASA Astrophysics Data System (ADS)
Sasanpour, Pezhman; Mohammadpour, Raheleh
Light scattering design in dye and quantum dot sensitized solar cells is one of the main concerns in enhancing their light harvesting efficiency, and also in improving their power conversion efficiency. Herein, we present a theoretical analysis to calculate the dependence of the light scattering efficiency in dye solar cells that have employed scattering agents with various sizes and morphologies incorporated in nanostructured photoanodes with different designs. Various isotropic and anisotropic nanostructures, including filled and hollow spheres, spherical voids, nanowires and hollow fibres in a size range of 100 nm to 900 nm, have been considered as scattering centres. The scattering materials are included in the photoanode of dye solar cells, either on top of the mesoporous layer or embedded in an active medium, and the scattering cross section has been calculated accordingly. The results indicate that employing hollow isotropic and anisotropic structures with thin wall thicknesses as a separate layer on top of the active meso-porous film may result in better scattering efficiency in the ultraviolet (UV) and visible wavelength range; however, a submicron filled sphere works better in near infrared (NIR) wavelength range. Incorporating anisotropic hollow fibres in the meso-porous photoelectrode will result in enhanced optical scattering features. The proposed model can provide a useful general framework for optimization of the photoanode of dye solar cells, employing various novel types of sensitizers.
Stainless steel optimization from quantum mechanical calculations
Levente Vitos; Pavel A. Korzhavyi; B÷rje Johansson
Alloy steel design has always faced a central problem: designing for a specific property very rarely produces a simultaneous significant improvement in other properties. For instance, it is difficult to design a material that combines high values of two of the most important mechanical characteristics of metals, hardness and ductility. Here we use the most recent quantum theories of random
Accurate rotational barrier calculations with diffusion quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Klahm, Sebastian; L³chow, Arne
Accurate quantum Monte Carlo, MP2, coupled cluster, and DFT calculations of rotational barriers of several small molecules are presented. With the diffusion quantum Monte Carlo method (DMC) excellent agreement with experimental barriers is obtained except for the gauche-gauche barriers of n-butane and ethylmethylether. It is argued that these two experimental values might be erroneous. Additionally, barriers calculated with the more efficient variational quantum Monte Carlo method (VMC) are presented. The VMC barriers are less accurate than the DMC results, but it is demonstrated that accurate barriers can be obtained with sophisticated Jastrow correlation functions.
Solution of quantum Langevin equation: approximations, theoretical and numerical aspects.
Banerjee, Dhruba; Bag, Bidhan Chandra; Banik, Suman Kumar; Ray, Deb Shankar
Based on a coherent state representation of noise operator and an ensemble averaging procedure using Wigner canonical thermal distribution for harmonic oscillators, a generalized quantum Langevin equation has been recently developed [Phys. Rev. E 65, 021109 (2002); 66, 051106 (2002)] to derive the equations of motion for probability distribution functions in c-number phase-space. We extend the treatment to explore several systematic approximation schemes for the solutions of the Langevin equation for nonlinear potentials for a wide range of noise correlation, strength and temperature down to the vacuum limit. The method is exemplified by an analytic application to harmonic oscillator for arbitrary memory kernel and with the help of a numerical calculation of barrier crossing, in a cubic potential to demonstrate the quantum Kramers' turnover and the quantum Arrhenius plot. PMID:15267831
Quantum mechanical calculation of spectral statistics of modified Kepler problem
Tao Ma; Rostislav Serota
Discrepancy between periodic orbit theory and numerical calculation of a modified Kepler problem is cleared by a quantum mechanical calculation. The diagonal approximation already gives a good fit for the numerical calculation. A better result yet is gained by considering the coherent interference between the classical periodic orbits and the Balian-Bloch term. This approach produces improved results for the rectangular billiards as well.
Vibrational Spectra and Quantum Calculations of Ethylbenzene
NASA Astrophysics Data System (ADS)
Wang, Jian; Qiu, Xue-jun; Wang, Yan-mei; Zhang, Song; Zhang, Bing
Normal vibrations of ethylbenzene in the first excited state have been studied using resonant two-photon ionization spectroscopy. The band origin of ethylbenzene of S1?S0 transition appeared at 37586 cm-1. A vibrational spectrum of 2000 cm-1 above the band origin in the first excited state has been obtained. Several chain torsions and normal vibrations are obtained in the spectrum. The energies of the first excited state are calculated by the time-dependent density function theory and configuration interaction singles (CIS) methods with various basis sets. The optimized structures and vibrational frequencies of the S0 and S1 states are calculated using Hartree-Fock and CIS methods with 6-311++G(2d,2p) basis set. The calculated geometric structures in the S0 and S1 states are gauche conformations that the symmetric plane of ethyl group is perpendicular to the ring plane. All the observed spectral bands have been successfully assigned with the help of our calculations.
Absorbing-like boundaries for quantum field theoretical grid simulations
NASA Astrophysics Data System (ADS)
Norris, S.; Vikartofsky, A.; Wagner, R. E.; Su, Q.; Grobe, R.
We introduce a computational method that permits us to increase the interaction time for quantum mechanical and quantum field theoretical simulations of multi-particle states on a finite space-time grid. In contrast to the usual approach where the unwanted portion of the wave function close to the grid boundaries is absorbed by a potential with a negative imaginary part, this method is unitary and therefore conserves the norm of the state. This technique is based on assigning particles close to the boundary a larger effective mass (or slower speed of light) such that the particles slow down and cannot re-enter the interaction zone. The method can therefore be applied to multi-particle states for which imaginary potential methods fail.
Characterizing quantum theory in terms of information-theoretic constraints
Rob Clifton; Jeffrey Bub; Hans Halvorson
We show that three fundamental information-theoretic constraints--the impossibility of superluminal information transfer between two physical systems by performing measurements on one of them, the impossibility of broadcasting the information contained in an unknown physical state, and the impossibility of unconditionally secure bit commitment--suffice to entail that the observables and state space of a physical theory are quantum-mechanical. We demonstrate the converse derivation in part, and consider the implications of alternative answers to a remaining open question about nonlocality and bit commitment.
Detailed discussions and calculations of quantum Regge calculus of Einstein-Cartan theory
Xue Shesheng [ICRANeT Piazzale della Repubblica, 10-65122, Pescara (Italy); Department of Physics, University of Rome 'Sapienza', Piazzale A. Moro 5, 00185, Rome (Italy)
This article presents detailed discussions and calculations of the recent paper 'Quantum Regge calculus of Einstein-Cartan theory' in [9]. The Euclidean space-time is discretized by a four-dimensional simplicial complex. We adopt basic tetrad and spin-connection fields to describe the simplicial complex. By introducing diffeomorphism and local Lorentz invariant holonomy fields, we construct a regularized Einstein-Cartan theory for studying the quantum dynamics of the simplicial complex and fermion fields. This regularized Einstein-Cartan action is shown to properly approach to its continuum counterpart in the continuum limit. Based on the local Lorentz invariance, we derive the dynamical equations satisfied by invariant holonomy fields. In the mean-field approximation, we show that the averaged size of 4-simplex, the element of the simplicial complex, is larger than the Planck length. This formulation provides a theoretical framework for analytical calculations and numerical simulations to study the quantum Einstein-Cartan theory.
Theoretical calculation of the acoustic force on a patterned silicon wafer during megasonic cleaning
Deymier, Pierre
Theoretical calculation of the acoustic force on a patterned silicon wafer during megasonic wafer immersed in water subjected to a megasonic beam. The method of calculation is based on a Green as a function of frequency and the angle the incident megasonic beam makes with the wafer surface
Nuclear Structure Calculations with Coupled Cluster Methods from Quantum Chemistry
NASA Astrophysics Data System (ADS)
Dean, D. J.; Gour, J. R.; Hagen, G.; Hjorth-Jensen, M.; Kowalski, K.; Papenbrock, T.; Piecuch, P.; W?och, M.
We present several coupled-cluster calculations of ground and excited states of 4He and 16O employing methods from quantum chemistry. A comparison of coupled cluster results with the results of exact diagonalization of the hamiltonian in the same model space and other truncated shell-model calculations shows that the quantum chemistry inspired coupled cluster approximations provide an excellent description of ground and excited states of nuclei, with much less computational effort than traditional large-scale shell-model approaches. Unless truncations are made, for nuclei like 16O, full-fledged shell-model calculations with four or more major shells are not possible. However, these and even larger systems can be studied with the coupled cluster methods due to the polynomial rather than factorial scaling inherent in standard shell-model studies. This makes the coupled cluster approaches, developed in quantum chemistry, viable methods for describing weakly bound systems of interest for future nuclear facilities.
Quantum mechanical cluster calculations of critical scintillationprocesses
Derenzo, Stephen E.; Klintenberg, Mattias K.; Weber, Marvin J.
This paper describes the use of commercial quantum chemistrycodes to simu-late several critical scintillation processes. The crystalis modeled as a cluster of typically 50 atoms embedded in an array oftypically 5,000 point charges designed to reproduce the electrostaticfield of the infinite crystal. The Schrodinger equation is solved for theground, ionized, and excited states of the system to determine the energyand electron wavefunction. Computational methods for the followingcritical processes are described: (1) the formation and diffusion ofrelaxed holes, (2) the formation of excitons, (3) the trapping ofelectrons and holes by activator atoms, (4) the excitation of activatoratoms, and (5) thermal quenching. Examples include hole diffusion in CsI,the exciton in CsI, the excited state of CsI:Tl, the energy barrier forthe diffusion of relaxed holes in CaF2 and PbF2, and prompt hole trappingby activator atoms in CaF2:Eu and CdS:Te leading to an ultra-fast (<50ps) scintillation risetime.
Crystal structure and theoretical calculations of Julocrotine, a natural product with antileishmanial activity
NASA Astrophysics Data System (ADS)
Moreira, Rafael Y. O.; Brasil, Davi S. B.; Alves, Clßudio N.; Guilhon, Giselle M. S. P.; Santos, Lourivaldo S.; Arruda, Mara S. P.; M³ller, Adolfo H.; Barbosa, PatrĒcia S.; Abreu, Alcicley S.; Silva, Edilene O.; Rumjanek, Victor M.; Souza, Jaime, Jr.; da Silva, Albķrico B. F.; Santos, Regina H. De A.
Julocrotine, N-(2,6-dioxo-1-phenethyl-piperidin-3-yl)-2-methyl-butyramide, is a potent antiproliferative agent against the promastigote and amastigote forms of Leishmania amazonensis (L.). In this work, the crystal structure of Julocrotine was solved by X-ray diffraction, and its geometrical parameters were compared with theoretical calculations at the B3LYP and HF level of theory. IR and NMR spectra also have been obtained and compared with theoretical calculations. IR absorptions calculated with the B3LYP level of theory employed together with the 6-311G+(d,p) basis set, are close to those observed experimentally. Theoretical NMR calculations show little deviation from experimental results. The results show that the theory is in accordance with the experimental data.0
Quantum calculations of H2-H2 collisions: from ultracold to thermal energies.
Quķmķner, Goulven; Balakrishnan, Naduvalath
We present quantum dynamics of collisions between two para-H(2) molecules from low (10(-3) K) to high collision energies (1 eV). The calculations are carried out using a quantum scattering code that solves the time-independent Schrodinger equation in its full dimensionality without any decoupling approximations. The six-dimensional potential energy surface for the H(4) system developed by Boothroyd et al. [J. Chem. Phys. 116, 666 (2002)] is used in the calculations. Elastic, inelastic, and state-to-state cross sections as well as rate coefficients from T=1 K to 400 K obtained from our calculations are compared with available experimental and theoretical results. Overall, good agreement is obtained with previous studies. PMID:19317535
Macroscopic quantum-type potentials in theoretical systems biology.
Nottale, Laurent
We review in this paper the use of the theory of scale relativity and fractal space-time as a tool particularly well adapted to the possible development of a future genuine systems theoretical biology. We emphasize in particular the concept of quantum-type potentials, since, in many situations, the effect of the fractality of space-or of the underlying medium-can be reduced to the addition of such a potential energy to the classical equations of motion. Various equivalent representations-geodesic, quantum-like, fluid mechanical, stochastic-of these equations are given, as well as several forms of generalized quantum potentials. Examples of their possible intervention in high critical temperature superconductivity and in turbulence are also described, since some biological processes may be similar in some aspects to these physical phenomena. These potential extra energy contributions could have emerged in biology from the very fractal nature of the medium, or from an evolutive advantage, since they involve spontaneous properties of self-organization, morphogenesis, structuration and multi-scale integration. Finally, some examples of applications of the theory to actual biological-like processes and functions are also provided. PMID:24709901
Theoretical and experimental studies of (In,Ga)As/GaP quantum dots.
Robert, Cedric; Thanh, Tra Nguyen; Cornet, Charles; Turban, Pascal; Perrin, Mathieu; Balocchi, Andrea; Folliot, Herve; Bertru, Nicolas; Pedesseau, Laurent; Nestoklon, Mikhail O; Even, Jacky; Jancu, Jean-Marc; Tricot, Sylvain; Durand, Olivier; Marie, Xavier; Le Corre, Alain
(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of kĘp and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types. PMID:23176537
Theoretical and experimental studies of (In,Ga)As/GaP quantum dots
(In,Ga)As/GaP(001) quantum dots (QDs) are grown by molecular beam epitaxy and studied both theoretically and experimentally. The electronic band structure is simulated using a combination of kĘp and tight-binding models. These calculations predict an indirect to direct crossover with the In content and the size of the QDs. The optical properties are then studied in a low-In-content range through photoluminescence and time-resolved photoluminescence experiments. It suggests the proximity of two optical transitions of indirect and direct types. PMID:23176537
A theoretical study of blue phosphorene nanoribbons based on first-principles calculations
Xie, Jiafeng; Si, M. S., E-mail: firstname.lastname@example.com; Yang, D. Z.; Zhang, Z. Y.; Xue, D. S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)
Based on first-principles calculations, we present a quantum confinement mechanism for the band gaps of blue phosphorene nanoribbons (BPNRs) as a function of their widths. The BPNRs considered have either armchair or zigzag shaped edges on both sides with hydrogen saturation. Both the two types of nanoribbons are shown to be indirect semiconductors. An enhanced energy gap of around 1?eV can be realized when the ribbon's width decreases to ?10?┼. The underlying physics is ascribed to the quantum confinement effect. More importantly, the parameters to describe quantum confinement are obtained by fitting the calculated band gaps with respect to their widths. The results show that the quantum confinement in armchair nanoribbons is stronger than that in zigzag ones. This study provides an efficient approach to tune the band gap in BPNRs.
Theoretical investigations on molecular structure, vibrational spectra, HOMO, LUMO, NBO analysis and hyperpolarizability calculations of thiophene-2-carbohydrazide.
Balachandran, V; Janaki, A; Nataraj, A
The Fourier-Transform infrared and Fourier-Transform Raman spectra of thiophene-2-carbohydrazide (TCH) was recorded in the region 4000-400 cm(-1) and 3500-100 cm(-1). Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of TCH were carried out by DFT (B3LYP) method with 6-311++G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. Stability of the molecule arising from hyper conjugative interaction and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. UV spectrum was measured in different solvent. The energy and oscillator strength are calculated by Time Dependant Density Functional Theory (TD-DFT) results. The calculated HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The complete assignments were performed on the basis of the potential energy distribution (PED) of vibrational modes, calculated with scaled quantum mechanics (SQM) method. Finally the theoretical FT-IR, FT-Raman, and UV spectra of the title molecule have also been constructed. PMID:24060478
Photoluminescence transitions in semiconductor superlattices. Theoretical calculations for InGaN blue laser device
A. Kunold; P. Pereyra
The optical response of an AlGaN\\/GaN\\/(InxGa1-xN)n\\/GaN\\/AlGaN heterostructure is obtained from precise, and comparatively simple, transition probability calculations. A comprehensive approach to evaluate these quantities from rigorous expressions of the heterostructure's energy eigenvalues and eigenfunctions is given. Taking full account of the longitudinal quantum wells and the lateral quantum dot confinement, quite precise intraband energy levels and wave functions have been
Quantum Monte Carlo calculations of symmetric nuclear matter
Stefano Gandolfi; Francesco Pederiva; Stefano Fantoni; Kevin E. Schmidt
We present an accurate numerical study of the equation of state of nuclear matter based on realistic nucleon--nucleon interactions by means of Auxiliary Field Diffusion Monte Carlo (AFDMC) calculations. The AFDMC method samples the spin and isospin degrees of freedom allowing for quantum simulations of large nucleonic systems and can provide quantitative understanding of problems in nuclear structure and astrophysics.
Calculating Potential Energy Curves with Quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Powell, Andrew D.; Dawes, Richard
Quantum Monte Carlo (QMC) is a computational technique that can be applied to the electronic Schr÷dinger equation for molecules. QMC methods such as Variational Monte Carlo (VMC) and Diffusion Monte Carlo (DMC) have demonstrated the capability of capturing large fractions of the correlation energy, thus suggesting their possible use for high-accuracy quantum chemistry calculations. QMC methods scale particularly well with respect to parallelization making them an attractive consideration in anticipation of next-generation computing architectures which will involve massive parallelization with millions of cores. Due to the statistical nature of the approach, in contrast to standard quantum chemistry methods, uncertainties (error-bars) are associated with each calculated energy. This study focuses on the cost, feasibility and practical application of calculating potential energy curves for small molecules with QMC methods. Trial wave functions were constructed with the multi-configurational self-consistent field (MCSCF) method from GAMESS-US.[1] The CASINO Monte Carlo quantum chemistry package [2] was used for all of the DMC calculations. An overview of our progress in this direction will be given. References: M. W. Schmidt et al. J. Comput. Chem. 14, 1347 (1993). R. J. Needs et al. J. Phys.: Condensed Matter 22, 023201 (2010).
Quantum dynamics of chemical reactions by converged algebraic variational calculations
Donald G. Truhlar; David W. Schwenke; Donald J. Kouri
This paper describes recent progress in using algebraic variational methods and L┬▓ basis sets for converged quantum mechanical calculations of chemical reaction dynamics of the H + HŌ, O + HŌ, H + HBr, and F + HŌ reactions and the isotopically substituted reactions D + HŌ and O + HD and some of the reverse reactions. The paper emphasizes
INFOBITS: A Visual Basic program for calculating information theoretic statistics from behavior sequences
D. W. Dunham; M. Sherba; P. Rutherford
We describe a Visual Basic add-in macro program for Microsoft Excel 5 and 7 (and later versions) that calculates basic, first-order,\\u000a information theoretic statistics from matrices based on behavior sequences, such as those from animal or human interaction\\u000a studies. Information theoretic statistics measure association between behavioral events in bits, a unit that is independent\\u000a of the particular system under study.
Theoretical calculation and vibrational spectral analysis of L-arginine trifluoroacetate
NASA Astrophysics Data System (ADS)
Sun, Z. H.; Zhang, L.; Xu, D.; Wang, X. Q.; Liu, X. J.; Zhang, G. H.
Fourier transform infrared and Raman spectra of the nonlinear optical crystal, L-arginine trifluoroacetate ( L-arginineĘCF 3COOH, abbreviated as LATF) have been calculated by the first-principles calculation and investigated in experiment. The calculated results are slightly different from those experimental values because of the distinction resulted from the intermolecular hydrogen bonds. The role of this type of intermolecular interaction on the crystal vibrational spectra and nonlinear optical properties has been discussed. The absorption-edge on the IR side has been estimated by the theoretical approach on basis of the calculated infrared spectrum, which will be meaningful for further research on NLO crystal.
Quantum field theoretic approach to neutrino oscillations in matter
Evgeny Kh. Akhmedov; Alina Wilhelm
We consider neutrino oscillations in non-uniform matter in a quantum field theoretic (QFT) approach, in which neutrino production, propagation and detection are considered as a single process. We find the conditions under which the oscillation probability can be sensibly defined and demonstrate how the properly normalized oscillation probability can be obtained in the QFT framework. We derive the evolution equation for the oscillation amplitude and discuss the conditions under which it reduces to the standard Schr\\"odinger-like evolution equation. It is shown that, contrary to the common usage, the Schr\\"odinger-like evolution equation is not applicable in certain cases, such as oscillations of neutrinos produced in decays of free pions provided that sterile neutrinos with $\\Delta m^2\\gtrsim 1$ eV$^2$ exist.
Efficient method for the calculation of dissipative quantum transport in quantum cascade lasers.
Greck, Peter; Birner, Stefan; Huber, Bernhard; Vogl, Peter
We present a novel and very efficient method for calculating quantum transport in quantum cascade lasers (QCLs). It follows the nonequilibrium Green's function (NEGF) framework but sidesteps the calculation of lesser self-energies by replacing them by a quasi-equilibrium expression. This method generalizes the phenomenological B³ttiker probe model by taking into account individual scattering mechanisms. It is orders of magnitude more efficient than a fully self-consistent NEGF calculation for realistic devices. We apply this method to a new THz QCL design which works up to 250 K - according to our calculations. PMID:25836876
New method for calculating binding energies in quantum mechanics and quantum field theories
Gat, G.; Rosenstein, B. (Department of Physics, University of Maryland, College Park, Maryland 20742 (United States) Institute of Physics, Academia Sinica, Taipei, 11529 (Taiwan))
We propose a systematic perturbative method for calculating the binding energy of threshold bound states---states which exist for arbitrary small coupling. The starting point is a (regularized) free theory. Explicit calculations are performed for quantum mechanics with arbitrary short-range potential in 1D and various (1+1)-dimensional quantum field theories. We check the method by comparing the results with exact formulas available in solvable models.
Efficient hybrid-symbolic methods for quantum mechanical calculations
NASA Astrophysics Data System (ADS)
Scott, T. C.; Zhang, Wenxing
We present hybrid symbolic-numerical tools to generate optimized numerical code for rapid prototyping and fast numerical computation starting from a computer algebra system (CAS) and tailored to any given quantum mechanical problem. Although a major focus concerns the quantum chemistry methods of H. Nakatsuji which has yielded successful and very accurate eigensolutions for small atoms and molecules, the tools are general and may be applied to any basis set calculation with a variational principle applied to its linear and non-linear parameters.
Uncertainties Associated with Theoretically Calculated N2-Broadened Half-Widths of H2O Lines
Gamache, Robert R.
1 Uncertainties Associated with Theoretically Calculated N2- Broadened Half-Widths of H2O Lines Q-broadend Lorentzian half-widths of the H2O lines using the modified Robert-Bonamy formalism. Based the uncertainty associated with them. One can divide all H2O lines into three categories: large, intermediate
Efficiency and power loss in d. c. chopper circuits. [Theoretical calculation
Beck, M.O.
The object of this paper was to investigate the efficiency and source of power losses of various classes of dc chopper circuits. The study involved a theoretical calculation of the power losses, supported by a considerable amount of practical work on full power-rated traction motor test bed. 3 refs.
Metal Vapors in Gas Tungsten Arcs: Part II. Theoretical Calculations of Transport Properties
Eagar, Thomas W.
( ( Metal Vapors in Gas Tungsten Arcs: Part II. Theoretical Calculations of Transport Properties G, if the presence of other metal vapors such as iron or manganese is also considered. It is therefore concluded, the effects of vapors emitted by the tungsten electrode may have a great effect on arc properties
Quantum Monte Carlo Calculations in Solids with Downfolded Hamiltonians
NASA Astrophysics Data System (ADS)
Ma, Fengjie; Purwanto, Wirawan; Zhang, Shiwei; Krakauer, Henry
We present a combination of a downfolding many-body approach with auxiliary-field quantum Monte Carlo (AFQMC) calculations for extended systems. Many-body calculations operate on a simpler Hamiltonian which retains material-specific properties. The Hamiltonian is systematically improvable and allows one to dial, in principle, between the simplest model and the original Hamiltonian. As a by-product, pseudopotential errors are essentially eliminated using frozen orbitals constructed adaptively from the solid environment. The computational cost of the many-body calculation is dramatically reduced without sacrificing accuracy. Excellent accuracy is achieved for a range of solids, including semiconductors, ionic insulators, and metals. We apply the method to calculate the equation of state of cubic BN under ultrahigh pressure, and determine the spin gap in NiO, a challenging prototypical material with strong electron correlation effects.
An experimental and theoretical mechanistic study of biexciton quantum yield enhancement in single quantum dots near gold nanoparticles
NASA Astrophysics Data System (ADS)
Dey, Swayandipta; Zhou, Yadong; Tian, Xiangdong; Jenkins, Julie A.; Chen, Ou; Zou, Shengli; Zhao, Jing
In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures.In this work, we systematically investigated the plasmonic effect on blinking, photon antibunching behavior and biexciton emission of single CdSe/CdS core/shell quantum dots (QDs) near gold nanoparticles (NPs) with a silica shell (Au@SiO2). In order to obtain a strong interaction between the plasmons and excitons, the Au@SiO2 NPs and CdSe/CdS QDs of appropriate sizes were chosen so that the plasmon resonance overlaps with the absorption and emission of the QDs. We observed that in the regime of a low excitation power, the photon antibunching and blinking properties of single QDs were modified significantly when the QDs were on the Au@SiO2 substrates compared to those on glass. Most significantly, second-order photon intensity correlation data show that the presence of plasmons increases the ratio of the biexciton quantum yield over the exciton quantum yield (QYBX/QYX). An electrodynamics model was developed to quantify the effect of plasmons on the lifetime, quantum yield, and emission intensity of the biexcitons for the QDs. Good agreement was obtained between the experimentally measured and calculated changes in QYBX/QYX due to Au@SiO2 NPs, showing the validity of the developed model. The theoretical studies also indicated that the relative position of the QDs to the Au NPs and the orientation of the electric field are important factors that regulate the emission properties of the excitons and biexcitons of QDs. The study suggests that the multiexciton emission efficiency in QD systems can be manipulated by employing properly designed plasmonic structures. Electronic supplementary information (ESI) available: The calculation of
Wavelength dependence of nitrate radical quantum yield from peroxyacetyl nitrate photolysis: experimental and theoretical studies.
Flowers, Bradley A; Stanton, John F; Simpson, William R
The photolysis wavelength dependence of the nitrate radical quantum yield for peroxyacetyl nitrate (CH(3)C(O)OONO(2), PAN) is investigated. The wavelength range used in this work is between 289 and 312 nm, which mimics the overlap of the solar flux available in the atmosphere and PAN's absorption cross section. We find the nitrate radical quantum yield from PAN photolysis to be essentially invariant; Phi(NO3)(PAN) = 0.30 +/- 0.07 (+/-2sigma) in this region. The excited states involved in PAN photolysis are also investigated using ab initio calculations. In addition to PAN, calculations on peroxy nitric acid (HOONO(2), PNA) are performed to examine general photochemical properties of the -OONO(2) chromophore. Equation of motion coupled cluster calculations (EOM-CCSD) are used to examine excited state energy gradients for the internal coordinates, oscillator strengths, and transition energies for the n --> pi* transitions responsible for the photolysis of both PNA and PAN. We find in both molecules, photodissociation of both O-O and O-N bonds occurs via excitation to predissociative electronic excited states and subsequent redistribution of that energy as opposed to directly dissociative excitations. Comparison and contrast between experimental and theoretical studies of HOONO(2) and PAN photochemistry from this and other work provide unique insight on the photochemistry of these species in the atmosphere. PMID:17958340
A Quantum Theoretical Explanation for Probability Judgment Errors Jerome R. Busemeyer
Busemeyer, Jerome R.
computer; rather, we only use quantum principles to derive cog- nitive models and leave the neural basisA Quantum Theoretical Explanation for Probability Judgment Errors Jerome R. Busemeyer Indiana University A quantum probability model is introduced and used to explain human probability judgment errors
Rotational isomerism of some chloroacetamides: theoretical and experimental studies through calculations, infrared and NMR.
Santos, Marcela F; Braga, Carolyne B; Rozada, Thiago C; Basso, Ernani A; Fiorin, Barbara C
The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (ClCCO) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and (13)C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. (1)JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend. PMID:24727174
On kaonic hydrogen. Phenomenological quantum field theoretic model revisited
NASA Astrophysics Data System (ADS)
Ivanov, A. N.; Cargnelli, M.; Faber, M.; Fuhrmann, H.; Ivanova, V. A.; Marton, J.; Troitskaya, N. I.; Zmeskal, J.
We argue that due to isospin and U-spin invariance of strong low-energy interactions the S-wave scattering lengths a 0 0 and a 1 0 of »N scattering with isospin I = 0 and I = 1 satisfy the low-energy theorem a 0 0 +3a 1 0 = 0 valid to leading order in chiral expansion. In the model of strong low-energy »N interactions at threshold (Eur. Phys. J. A 21, 11 (2004)) we revisit the contribution of the ?(1750) resonance, which does not saturate the low-energy theorem a 0 0 +3a 1 0 = 0, and replace it by the baryon background with properties of an SU(3) octet. We calculate the S-wave scattering amplitudes of K-N and K-d scattering at threshold. We calculate the energy level displacements of the ground states of kaonic hydrogen and deuterium. The result obtained for kaonic hydrogen agrees well with recent experimental data by the DEAR Collaboration. We analyse the cross-sections for elastic and inelastic K-p scattering for laboratory momenta 70MeV/c < p K < 150MeV/c of the incident K--meson. The theoretical results agree with the available experimental data within two standard deviations.
Energy from CO2 using capacitive electrodes--theoretical outline and calculation of open circuit voltage.
Paz-Garcia, J M; Schaetzle, O; Biesheuvel, P M; Hamelers, H V M
Recently, a new technology has been proposed for the utilization of energy from CO2 emissions (Hamelers et al., 2014). The principle consists of controlling the dilution process of CO2-concentrated gas (e.g., exhaust gas) into CO2-dilute gas (e.g., air) thereby extracting a fraction of the released mixing energy. In this paper, we describe the theoretical fundamentals of this technology when using a pair of charge-selective capacitive electrodes. We focus on the behavior of the chemical system consisting of CO2 gas dissolved in water or monoethanolamine solution. The maximum voltage given for the capacitive cell is theoretically calculated, based on the membrane potential. The different aspects that affect this theoretical maximum value are discussed. PMID:24461836
Theoretical calculation of plane wave speeds for alkali metals under pressure.
NASA Technical Reports Server (NTRS)
Eftis, J.; Macdonald, D. E.; Arkilic, G. M.
Theoretical calculations of the variation with pressure of small amplitude plane wave speeds are performed for sodium and potassium at zero temperature. The results obtained for wave speeds associated with volume dependent second-order elastic coefficients show better agreement with experimental data than for wave speeds associated with shear dependent coefficients. This result is believed to be due to omission of the band structure correction to the strain energy density.
Sub 100 nm proton beam micromachining: theoretical calculations on resolution limits
J. A. van Kan; T. C. Sum; T. Osipowicz; F. Watt
Proton beam micromachining is a novel direct-write process for the production of three-dimensional (3D) microstructures. A focused beam of MeV protons is scanned in a pre-determined pattern over a suitable resist material (e.g. PMMA or SU-8) and the latent image formed is subsequently developed chemically. In this paper calculations on theoretical resolution limits of proton beam micromachined three-dimensional microstructures are
Delay time calculation for dual-wavelength quantum cascade lasers
Hamadou, A., E-mail: firstname.lastname@example.com [Dķpartement des Sciences et Techniques, Facultķ des Sciences et de la Technologie, Universitķ de Bordj Bou Arreridj 34000 (Algeria); Laboratoire dÆķtude des surfaces et interfaces des matķriaux solides (LESIMS), Sķtif 19000 (Algeria); Lamari, S. [Laboratoire dÆķtude des surfaces et interfaces des matķriaux solides (LESIMS), Sķtif 19000 (Algeria); Dķpartement de Physique, Facultķ des Sciences, Universitķ Sķtif 1, 19000 (Algeria); Thobel, J.-L. [Institut d'Electronique, de Microķlectronique et de Nanotechnologie (IEMN), UMR 8520, Universitķ Lille1, Avenue Poincarķ, BP 60069, 59652 Villeneuve d'Ascq Cķdex (France)
In this paper, we calculate the turn-on delay (t{sub th}) and buildup (?t) times of a midinfrared quantum cascade laser operating simultaneously on two laser lines having a common upper level. The approach is based on the four-level rate equations model describing the variation of the electron number in the states and the photon number present within the cavity. We obtain simple analytical formulae for the turn-on delay and buildup times that determine the delay times and numerically apply our results to both the single and bimode states of a quantum cascade laser, in addition the effects of current injection on t{sub th} and ?t are explored.
The Nature of Infinity in Quantum Field Calculations
NASA Astrophysics Data System (ADS)
Kriske, Richard
In many textbooks on Quantum Field Theory it has been noted that an infinity is taken a circle and the flux is calculated from the A field in that manner. There are of course many such examples of this sort of calculation using infinity as a circle. This author would like to point out that if the three dimensions of space are curved and the one dimension of time is not, in say a four space, infinity is the horizon, which is not a circle but rather a sphere; as long as space-time is curved uniformly, smoothly and has positive curvature. This author believes the math may be in error, since maps of the CMBR seem to indicate a ``Swiss-Cheese'' type of topology, wherein the Sphere at infinity (the Horizon of the Universe), has holes in it that can readily be seen. This author believes that these irregularities most certainly have a calculable effect on QED, QCD and Quantum Field Theory.
Theoretical study of auger recombination processes in deep quantum wells
Danilov, L. V., E-mail: email@example.com; Zegrya, G. G. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)], E-mail: email@example.com
The basic processes and mechanisms of Auger recombination of nonequilibrium carriers in a semiconductor heterostructure with deep InAs{sub 0.84}Sb{sub 0.16}/AlSb quantum wells (QWs) are analyzed. It is shown that a zero-threshold Auger recombination process involving two heavy holes predominates in sufficiently narrow QWs, and a resonant process involving two electrons is dominant in wide QWs. The range of QW widths at which the Auger recombination is suppressed in a given structure to the greatest extent (suppression region) is determined. In this case, the threshold process involving two electrons remains the basic nonradiative recombination process, with its probability being several orders of magnitude lower than those for the zero-threshold and resonant mechanisms. In turn, the zero-threshold mechanism involving two electrons is totally impossible in the heterostructure under study because of the large conduction-band offset (which markedly exceeds the energy gap). Also, the range of emission wavelengths that corresponds to the suppression region is estimated. It is shown that the interval calculated belongs to the mid-IR range.
Biological applications of hybrid quantum mechanics/molecular mechanics calculation.
Kang, Jiyoung; Hagiwara, Yohsuke; Tateno, Masaru
Since in most cases biological macromolecular systems including solvent water molecules are remarkably large, the computational costs of performing ab initio calculations for the entire structures are prohibitive. Accordingly, QM calculations that are jointed with MM calculations are crucial to evaluate the long-range electrostatic interactions, which significantly affect the electronic structures of biological macromolecules. A UNIX-shell-based interface program connecting the quantum mechanics (QMs) and molecular mechanics (MMs) calculation engines, GAMESS and AMBER, was developed in our lab. The system was applied to a metalloenzyme, azurin, and PU.1-DNA complex; thereby, the significance of the environmental effects on the electronic structures of the site of interest was elucidated. Subsequently, hybrid QM/MM molecular dynamics (MD) simulation using the calculation system was employed for investigation of mechanisms of hydrolysis (editing reaction) in leucyl-tRNA synthetase complexed with the misaminoacylated tRNA(Leu), and a novel mechanism of the enzymatic reaction was revealed. Thus, our interface program can play a critical role as a powerful tool for state-of-the-art sophisticated hybrid ab initio QM/MM MD simulations of large systems, such as biological macromolecules. PMID:22536015
Importance of parametrizing constraints in quantum-mechanical variational calculations
NASA Technical Reports Server (NTRS)
Chung, Kwong T.; Bhatia, A. K.
In variational calculations of quantum mechanics, constraints are sometimes imposed explicitly on the wave function. These constraints, which are deduced by physical arguments, are often not uniquely defined. In this work, the advantage of parametrizing constraints and letting the variational principle determine the best possible constraint for the problem is pointed out. Examples are carried out to show the surprising effectiveness of the variational method if constraints are parameterized. It is also shown that misleading results may be obtained if a constraint is not parameterized.
Evolution of Black Carbon Optical Properties during Atmospheric Aging: Comparison Between Theoretical Calculations and Laboratory Experiments
NASA Astrophysics Data System (ADS)
He, C.; Liou, K. N.; Takano, Y.; Li, Q.; Yang, P.; Zhang, R.
The optical properties of black carbon (BC) are significantly affected by its aging process in the atmosphere. We have built a conceptual model defining three BC aging stages, including freshly emitted BC aggregates, coating by soluble material and hygroscopic growth. We apply an improved geometric-optics surface-wave approach (Liou et al., 2011; Takano et al., 2013) to calculate the absorption and scattering properties of BC at each stage and compare the theoretical results with those obtained from laboratory experiments (Zhang et al., 2008; Khalizov et al., 2009). Preliminary results show a general agreement between calculated and measured BC absorption cross sections (bias < 10%) and scattering cross sections (bias < 30%) for BC aerosols with mobility diameters of 155, 245 and 320 nm at Stages 1 and 2, where BC is coated by sulfuric acid and its water solution, respectively. We find that the calculated scattering and absorption cross sections for fresh BC aggregates (Stage 0) with different sizes are invariably larger than experimental results partly because of the uncertainty in theoretical calculations for BC with size parameters less than 1. It appears that the uncertainty in the experiment could also contribute to the discrepancy, considering that the measuring instrument missed some scattering in certain angles (0-7░ and 170-180░). Finally, we will apply the conceptual model and the single-scattering results to assess the effects of BC aging processes on direct radiative forcing using observed BC vertical profiles.
The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft
NASA Technical Reports Server (NTRS)
Avrett, E. H.
Models and spectra of sunspots were studied, because they are important to energy balance and variability discussions. Sunspot observations in the ultraviolet region 140 to 168 nn was obtained by the NRL High Resolution Telescope and Spectrograph. Extensive photometric observations of sunspot umbrae and prenumbrae in 10 chanels covering the wavelength region 387 to 3800 nm were made. Cool star opacities and model atmospheres were computed. The Sun is the first testcase, both to check the opacity calculations against the observed solar spectrum, and to check the purely theoretical model calculation against the observed solar energy distribution. Line lists were finally completed for all the molecules that are important in computing statistical opacities for energy balance and for radiative rate calculations in the Sun (except perhaps for sunspots). Because many of these bands are incompletely analyzed in the laboratory, the energy levels are not well enough known to predict wavelengths accurately for spectrum synthesis and for detailed comparison with the observations.
Raman and infrared spectra and theoretical calculations of dipicolinic acid, dinicotinic acid, and their dianions
NASA Astrophysics Data System (ADS)
McCann, Kathleen; Laane, Jaan
The Raman and infrared spectra of dipicolinic acid (DPA) and dinicotinic acid (DNic) and their salts (CaDPA, Na 2DPA, and CaDNic) have been recorded and the spectra have been assigned. Ab initio and DFT calculations were carried out to predict the structures and vibrational spectra and were compared to the experimental results. Because of extensive intermolecular hydrogen bonding in the crystals of these molecules, the calculated structures and spectra for the individual molecules agree only moderately well with the experimental values. Theoretical calculations were also carried out for DPA dimers and DPAĘ2H 2O to better understand the intermolecular interactions. The spectra do show that DPA and its calcium salt, which are present in anthrax spores, can be distinguished from the very similar DNic and CaDNic.
Synthesis, crystal structure, vibrational spectra and theoretical calculation of 1-carboxymethyl-3-methylimidazolium chloride.
Xuan, Xiaopeng; Wang, Na; Xue, Zaikun
In this paper, the structure of 1-carboxymethyl-3-methylimidazolium chloride was studied by X-ray diffraction, density functional theory, and FT-IR and Raman spectroscopic techniques for the first time. Title compound crystallizes in the orthorhombic space group Pca2(1) with the cell dimensions a=13.445 (6) ┼, b=6.382 (3) ┼, c=9.727 (5) ┼ and V=834.6 (7) ┼(3). All the geometrical parameters have been calculated using by B3LYP with 6-311G++(d,p) basis set. Optimized geometries have been compared with the experimental data, and the hydrogen bond and short contact interactions were discussed. The vibrational frequencies, infrared intensities and Raman scattering activities of the title compound were calculated at the same level. The observed bands were assigned based on the theoretical calculations. The scaled vibrational frequencies seem to coincide with the experimental data with acceptable deviations. PMID:22728234
The successful merger of theoretical thermochemistry with fragment-based methods in quantum chemistry.
Ramabhadran, Raghunath O; Raghavachari, Krishnan
CONSPECTUS: Quantum chemistry and electronic structure theory have proven to be essential tools to the experimental chemist, in terms of both a priori predictions that pave the way for designing new experiments and rationalizing experimental observations a posteriori. Translating the well-established success of electronic structure theory in obtaining the structures and energies of small chemical systems to increasingly larger molecules is an exciting and ongoing central theme of research in quantum chemistry. However, the prohibitive computational scaling of highly accurate ab initio electronic structure methods poses a fundamental challenge to this research endeavor. This scenario necessitates an indirect fragment-based approach wherein a large molecule is divided into small fragments and is subsequently reassembled to compute its energy accurately. In our quest to further reduce the computational expense associated with the fragment-based methods and overall enhance the applicability of electronic structure methods to large molecules, we realized that the broad ideas involved in a different area, theoretical thermochemistry, are transferable to the area of fragment-based methods. This Account focuses on the effective merger of these two disparate frontiers in quantum chemistry and how new concepts inspired by theoretical thermochemistry significantly reduce the total number of electronic structure calculations needed to be performed as part of a fragment-based method without any appreciable loss of accuracy. Throughout, the generalized connectivity based hierarchy (CBH), which we developed to solve a long-standing problem in theoretical thermochemistry, serves as the linchpin in this merger. The accuracy of our method is based on two strong foundations: (a) the apt utilization of systematic and sophisticated error-canceling schemes via CBH that result in an optimal cutting scheme at any given level of fragmentation and (b) the use of a less expensive second layer of electronic structure method to recover all the missing long-range interactions in the parent large molecule. Overall, the work featured here dramatically decreases the computational expense and empowers the execution of very accurate ab initio calculations (gold-standard CCSD(T)) on large molecules and thereby facilitates sophisticated electronic structure applications to a wide range of important chemical problems. PMID:25393551
Nuclear-magnetic-resonance quantum calculations of the Jones polynomial
Marx, Raimund; Fahmy, Amr; Kauffman, Louis; Lomonaco, Samuel; Sp÷rl, Andreas; Pomplun, Nikolas; Schulte-Herbr³ggen, Thomas; Myers, John M.; Glaser, Steffen J.
The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots. PMID:21461143
Nuclear-magnetic-resonance quantum calculations of the Jones polynomial
Marx, Raimund; Spoerl, Andreas; Pomplun, Nikolas; Schulte-Herbrueggen, Thomas; Glaser, Steffen J. [Department of Chemistry, Technische Universitaet Muenchen, Lichtenbergstr. 4, D-85747 Garching (Germany); Fahmy, Amr [Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115 (United States); Kauffman, Louis [University of Illinois at Chicago, 851 S. Morgan Street, Chicago, Illinois 60607-7045 (United States); Lomonaco, Samuel [University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, Maryland 21250 (United States); Myers, John M. [Cruft Laboratory, Harvard University, 19 Oxford Street, Cambridge, Massachusetts 02138 (United States)
The repertoire of problems theoretically solvable by a quantum computer recently expanded to include the approximate evaluation of knot invariants, specifically the Jones polynomial. The experimental implementation of this evaluation, however, involves many known experimental challenges. Here we present experimental results for a small-scale approximate evaluation of the Jones polynomial by nuclear magnetic resonance (NMR); in addition, we show how to escape from the limitations of NMR approaches that employ pseudopure states. Specifically, we use two spin-1/2 nuclei of natural abundance chloroform and apply a sequence of unitary transforms representing the trefoil knot, the figure-eight knot, and the Borromean rings. After measuring the nuclear spin state of the molecule in each case, we are able to estimate the value of the Jones polynomial for each of the knots.
Theoretical calculation and experimental study of acousto-optically Q-switched CO2 laser.
Xie, Jijang; Guo, Ruhai; Li, Dianjun; Zhang, Chuansheng; Yang, Guilong; Geng, Yumin
Using resonator inserted with acousto-optically modulator, the experiments of the compacted CO(2) laser were performed with Q-switch. According to various factors that influenced the output of laser, the theoretical calculation of its main parameters was conducted by Q-switched pulsed laser rate equations. Based on the results, the technical route and approach were presented for optimization design of this laser. The measured peak power of this laser device was more than 4000W and pulsed width was 180ns which agreed well with the theoretical calculation. The range of repetition frequency could adjust from 1 Hz to 100 kHz. The theoretical analyzes and experimental results showed that the acoustic traveling time of ultrasonic field could not influence the pulse width of laser so that it did not require inserting optical lens in the cavity to reduce the diameter of beam. The acoustic traveling time only extended the establishingtime of laser pulse. The optimum working frequency of laser is about 1 kHz, which it matched with the radiation life time (1 ms) of CO(2) molecular upper energy level. When the frequency is above 1 kHz, the pulse width of laser increased with the frequency. The full band of wavelength tuning between 9.2 microm and 10.8 microm was obtained by grating selection one by one which the measured spectrum lines were over 30 in the condition of Q-switch. PMID:20588363
A comparison of theoretical methods of calculation of partition coefficients for selected drugs.
Pyka, Alina; Babu?ka, Magdalena; Zachariasz, Magdalena
Hundred ninety three drugs of different pharmacological activity were studied. Lipophilicity of a drug is one of the parameters, which influence its biological activity. The n-octanol-water partition coefficients were calculated for these compounds by use of different theoretical procedures (AlogPs, IAlogP, miLogP, ClogP, logP(Kowwin), and xlogP). Particular theoretical partition coefficients were compared with experimental n-octanol-water partition coefficients (logP(exp)) for all studied drugs. It was shown that experimental partition coefficients correlate the best with theoretical partition coefficients calculated by use of logP(Kowwin) and AlogPs methods. It was shown that it exists the possibility of the prediction of experimental n-octanol-water partition coefficients on the basis of logP(Kowwin), AlogPs, and ClogP for fifteen drugs (adrenalin, clobazam, 5,5-dimethylbarbituric acid, ethyl nicotinate, fluphenazine, ibuprofen, methyllorazepam, pimozide, prednisolone, promethazine, spironolactone, surital, theophylline, triamterene, and trimethoprim). PMID:20085219
Automated quantum conductance calculations using maximally-localised Wannier functions
Shelley, Matthew; Mostofi, Arash A; Marzari, Nicola
A robust, user-friendly, and automated method to determine quantum conductance in disordered quasi-one-dimensional systems is presented. The scheme relies upon an initial density- functional theory calculation in a specific geometry after which the ground-state eigenfunctions are transformed to a maximally-localised Wannier function (MLWF) basis. In this basis, our novel algorithms manipulate and partition the Hamiltonian for the calculation of coherent electronic transport properties within the Landauer-Buttiker formalism. Furthermore, we describe how short- ranged Hamiltonians in the MLWF basis can be combined to build model Hamiltonians of large (>10,000 atom) disordered systems without loss of accuracy. These automated algorithms have been implemented in the Wannier90 code[Mostofi et al, Comput. Phys. Commun. 178, 685 (2008)], which is interfaced to a number of electronic structure codes such as Quantum-ESPRESSO, AbInit, Wien2k, SIESTA and FLEUR. We apply our methods to an Al atomic chain with a Na defect...
Quantum electrodynamic calculation of quantum beats in a spontaneously radiating three level system
A. Schenzle; Richard G. Brewer
The coherence properties of a spontaneously radiating three-level atomic system are investigated in a first principle calculation that utilizes either coherent or incoherent preparation. Quantum beat phenomena are explained for the first time in a manner that reveals the statistical nature of the preparative step as well as a possible radiative correction to the beat frequency.
Rotational isomers, NBO and spectral analyses of N-(2-hydroxyethyl) phthalimide based on quantum chemical calculations
NASA Astrophysics Data System (ADS)
Lakshmi, A.; Balachandran, V.
FT-IR and FT-Raman spectra of N-(2-hydroxyethyl)phthalimide (NHEP) have been recorded and analyzed. The stable isomer of NHEP is determined. The optimization geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumber of NHEP have been investigated with the help of B3LYP scaled quantum mechanical (SQM) method. The infrared and Raman spectra were predicted theoretically from the calculated intensities. Natural bond orbital (NBO) analysis indicates the presence of Cdbnd O⋯H in the molecule. The calculated HOMO and LUMO are important in determining such properties as molecular reactivity. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron density isosurface with electrostatic potential (ESP).
Potassium-uracil/thymine ring cleavage enhancement as studied in electron transfer experiments and theoretical calculations.
Almeida, D; Bacchus-Montabonel, M-C; da Silva, F Ferreira; GarcĒa, G; LimŃo-Vieira, P
We report experimental and theoretical studies on ring cleavage enhancement in collisions of potassium atoms with uracil/thymine to further increase the understanding of the complex mechanisms yielding such fragmentation pathways. In these electron transfer processes time-of-flight (TOF) negative ion mass spectra were obtained in the collision energy range 13.5-23.0 eV. We note that CNO(-) is the major ring breaking anion formed and its threshold formation is discussed within the collision energy range studied. Such a decomposition process is supported by the first theoretical calculations to clarify how DNA/RNA pyrimidine base fragmentation is enhanced in electron transfer processes yielding ion-pair formation. PMID:24818533
Calculation of control coefficients of metabolic pathways. A flux-oriented graph-theoretic approach.
Sen, A K
Within the premises of the flux-oriented theory of Crabtree & Newsholme [(1987) Biochem. J. 247, 113-120], I have used a graph-theoretic approach for calculating the Control Coefficients of metabolic pathways. It is shown that a directed graph representing the control structure of a metabolic pathway can be constructed in a heuristic manner directly from the reaction diagram of the pathway, without the necessity of writing down the governing equations for the Control Coefficients. The Control Coefficients are derived from an analysis of the topology of the directed graph. The graph-theoretic approach also provides a visual framework for analysing the functional relationships of the individual enzymes. The control structures of the following pathways are examined here: (a) a simple unbranched pathway with four enzymes, (b) a simple branched pathway with three enzymes, and (c) a branched pathway with both carbon and energy (ATP) fluxes. PMID:1930155
Theoretical calculation of the melting curve of Cu-Zr binary alloys
NASA Astrophysics Data System (ADS)
Gunawardana, K. G. S. H.; Wilson, S. R.; Mendelev, M. I.; Song, Xueyu
Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. Our theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu51Zr14 (? ), CuZr(B2), CuZr2(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions.
A simple theoretical approach to calculate the electrical conductivity of nonideal copper plasma
Zaghloul, Mofreh R. [Department of Physics, College of Sciences, United Arab Emirates University, P.O.B. 17551, Al-Ain (United Arab Emirates)
A simple theoretical approach to calculate the electrical conductivity of partially ionized nonideal copper plasma is introduced. The densities of plasma species are calculated, to machine accuracy, including electronic excitation and allowing for high ionization states up to the atomic number of the element. Depression of ionization energies is taken into account using an interpolation formula that is valid over a wide range of densities. The formula yields the results of the Debye-Hueckel and the ion-sphere models at the limiting boundaries of low and high densities, respectively. The nonideal Coulomb logarithm is represented by an analytic wide-range formula supplemented by a specially tailored cutoff parameter. Effects of excluding excited and high ionization states on the calculation of ionization equilibrium and electrical conductivity of copper are investigated and assessed. Computational results of the electrical conductivity are compared with results from other theoretical models and available experimental measurements and showed reasonable agreement. A discussion about the choice of the ion-sphere radius is included and concerns about thermodynamic inconsistency when using the modified nonideal Saha equations are discussed and cleared.
Theoretical calculation of the melting curve of Cu-Zr binary alloys.
Gunawardana, K G S H; Wilson, S R; Mendelev, M I; Song, Xueyu
Helmholtz free energies of the dominant binary crystalline solids found in the Cu-Zr system at high temperatures close to the melting curve are calculated. Our theoretical approach combines fundamental measure density functional theory (applied to the hard-sphere reference system) and a perturbative approach to include the attractive interactions. The studied crystalline solids are Cu(fcc), Cu_{51}Zr_{14}(?), CuZr(B2), CuZr_{2}(C11b), Zr(hcp), and Zr(bcc). The calculated Helmholtz free energies of crystalline solids are in good agreement with results from molecular-dynamics (MD) simulations. Using the same perturbation approach, the liquid phase free energies are calculated as a function of composition and temperature, from which the melting curve of the entire composition range of this system can be obtained. Phase diagrams are determined in this way for two leading embedded atom method potentials, and the results are compared with experimental data. Theoretical melting temperatures are compared both with experimental values and with values obtained directly from MD simulations at several compositions. PMID:25493799
Determination of Absolute Configuration of Natural Products: Theoretical Calculation of Electronic Circular Dichroism as a Tool
Li, Xing-Cong; Ferreira, Daneel; Ding, Yuanqing
Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the past decade, the time dependent density functional theory (TDDFT) calculation of electronic circular dichroism (ECD) spectra has emerged as a very promising tool. The principle is simply based on the comparison of the calculated and experimental ECD spectra: the more closely they match, the more reliable conclusion for the AC assignment can be drawn. This review attempts to use several examples representing monomeric flavonoids, rotationally restricted biflavonoids, complex hexahydroxydiphenoyl-containing flavonoids, conformationally flexible and restrained sesquiterpenoids, cembrane-africanene terpenoids, dihydropyranocoumarins, alkaloids, and dihydroxanthones to illustrate the applicability of this approach in determining the AC of structurally diverse natural products. The findings clearly indicate that the TDDFT calculation of ECD spectra can quantify the contribution of individual conformers and the interaction of multiple chromophores, making it possible to determine the AC of complex chiral molecules. The calculated electronic transitions and molecular orbitals provide new insight into the interpretation of ECD spectra at the molecular level. PMID:24729741
A Quantum Theoretical Explanation for Probability Judgment Errors
ERIC Educational Resources Information Center
Busemeyer, Jerome R.; Pothos, Emmanuel M.; Franco, Riccardo; Trueblood, Jennifer S.
A quantum probability model is introduced and used to explain human probability judgment errors including the conjunction and disjunction fallacies, averaging effects, unpacking effects, and order effects on inference. On the one hand, quantum theory is similar to other categorization and memory models of cognition in that it relies on vectorģ
Improved quantum Monte Carlo calculation of the ground-state energy of the hydrogen molecule
Anderson, James B.
Improved quantum Monte Carlo calculation of the ground-state energy of the hydrogen molecule Bin more accurate than that of previous quantum Monte Carlo calculations. The energy is less accurate than predictions has most often been the analytic variational method, but the quantum Monte Carlo method has
Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom
Anderson, James B.
Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom Arne Lu, Pennsylvania 16802 Received 21 March 1996; accepted 11 June 1996 Quantum Monte Carlo calculations of the ground-node Green's function quantum Monte Carlo method the lowest upper bounds to the ground state energies to date
Configuration and conformation of alfentanil hydrochloride. Conformational study by NMR and theoretical calculations.
Jaime, Carlos; Virgili, Albert; Portillo, Susana; Caparr¾s, Antoni; Burusco, Kepa K
The configurational and conformational structure of alfentanil hydrochloride (1) was studied by nuclear magnetic resonance and theoretical calculations. Compound 1 is best described by equilibrium between two stereoisomeric piperidinium rings with the N-substituent always being in equatorial position. Nuclear magnetic resonance spectra demonstrate that, depending on the solvent, 1 adopts the conformation with an axial methoxymethylene group. Computations were crucial in determining the importance of the transannular attractive interaction between the positive charge at the piperidinium N-atom and the methoxymethyl group in position 4. PMID:24889875
Molecular structures of benzoic acid and 2-hydroxybenzoic acid, obtained by gas-phase electron diffraction and theoretical calculations.
Aarset, Kirsten; Page, Elizabeth M; Rice, David A
The structures of benzoic acid (C6H5COOH) and 2-hydroxybenzoic acid (C6H4OHCOOH) have been determined in the gas phase by electron diffraction using results from quantum chemical calculations to inform restraints used on the structural parameters. Theoretical methods (HF and MP2/6-311+G(d,p)) predict two conformers for benzoic acid, one which is 25.0 kJ mol(-1) (MP2) lower in energy than the other. In the low-energy form, the carboxyl group is coplanar with the phenyl ring and the O-H group eclipses the C=O bond. Theoretical calculations (HF and MP2/6-311+G(d,p)) carried out for 2-hydroxybenzoic acid gave evidence for seven stable conformers but one low-energy form (11.7 kJ mol(-1) lower in energy (MP2)) which again has the carboxyl group coplanar with the phenyl ring, the O-H of the carboxyl group eclipsing the C=O bond and the C=O of the carboxyl group oriented toward the O-H group of the phenyl ring. The effects of internal hydrogen bonding in 2-hydroxybenzoic acid can be clearly observed by comparison of pertinent structural parameters between the two compounds. These differences for 2-hydroxybenzoic acid include a shorter exocyclic C-C bond, a lengthening of the ring C-C bond between the substituents, and a shortening of the carboxylic single C-O bond. PMID:16836466
Molecular thermodynamics of metabolism: quantum thermochemical calculations for key metabolites.
Hadadi, N; Ataman, M; Hatzimanikatis, V; Panayiotou, C
The present work is the first of a series of papers aiming at a coherent and unified development of the thermodynamics of metabolism and the rationalization of feasibility analysis of metabolic pathways. The focus in this part is on high-level quantum chemical calculations of the thermochemical quantities of relatively heavy metabolites such as amino acids/oligopeptides, nucleosides, saccharides and their derivatives in the ideal gas state. The results of this study will be combined with the corresponding hydration/solvation results in subsequent parts of this work in order to derive the desired thermochemical quantities in aqueous solutions. The above metabolites exist in a vast conformational/isomerization space including rotational conformers, tautomers or anomers exhibiting often multiple or cooperative intramolecular hydrogen bonding. We examine the challenges posed by these features for the reliable estimation of thermochemical quantities. We discuss conformer search, conformer distribution and averaging processes. We further consider neutral metabolites as well as protonated and deprotonated metabolites. In addition to the traditional presentation of gas-phase acidities, basicities and proton affinities, we also examine heats and free energies of ionic species. We obtain simple linear relations between the thermochemical quantities of ions and the formation quantities of their neutral counterparts. Furthermore, we compare our calculations with reliable experimental measurements and predictive calculations from the literature, when available. Finally, we discuss the next steps and perspectives for this work. PMID:25799954
Pseudopotentials for quantum Monte Carlo calculations of transition metal oxides
NASA Astrophysics Data System (ADS)
Krogel, Jaron; Santana, Juan; Kent, Paul; Reboredo, Fernando
Quantum Monte Carlo calculations of transition metal oxides are partially limited by the availability of high quality pseudopotentials that are both accurate in QMC and compatible with major electronic structure codes, e.g. by not being overly hard in the standard planewave basis. Following insight gained from recent GW calculations, a set of neon core pseudopotentials with small cutoff radii have been created for the early transition metal elements Sc to Zn within the local density approximation of DFT. The pseudopotentials have been tested for energy consistency within QMC by calculating the first through fourth ionization potentials of the isolated transition metal (TM) atoms and the binding curve of each TM-O dimer. The vast majority of the ionization potentials fall within 0.3 eV of the experimental values, with exceptions occurring mainly for atoms with multiple unpaired d electrons where multireference effects are the strongest. The equilibrium bond lengths of the dimers are within 1% of experimental values and the binding energy errors are typically less than 0.3 eV. Given the uniform treatment of the core, the larger deviations occasionally observed may primarily reflect the limitations of a Slater-Jastrow trial wavefunction. This work is supported by the Materials Sciences & Engineering Division of the Office of Basic Energy Sciences, U.S. DOE. Research by PRCK was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.
Theoretical and experimental calculations, Mulliken charges and thermodynamic properties of 4-chloro-2-nitroanisole
NASA Astrophysics Data System (ADS)
Arunagiri, C.; Arivazhagan, M.; Subashini, A.; Maruthaiveeran, N.
The FT-IR and FT-Raman spectra of 4-chloro-2-nitroanisole were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the GAUSSIAN 09 package of programs using the B3LYP/6-311G(d,p) and 6-311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizability, NBO, HOMO-LUMO, NMR, UV, infrared intensities and Raman intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in good agreement with the values of similar structures.
Theoretical and experimental calculations, Mulliken charges and thermodynamic properties of 4-chloro-2-nitroanisole.
Arunagiri, C; Arivazhagan, M; Subashini, A; Maruthaiveeran, N
The FT-IR and FT-Raman spectra of 4-chloro-2-nitroanisole were recorded and analyzed. The vibrational wavenumbers were examined theoretically with the aid of the GAUSSIAN 09 package of programs using the B3LYP/6-311G(d,p) and 6-311++G(d,p) levels of theory. The data obtained from vibrational wavenumber calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied molecule. The first hyperpolarizability, NBO, HOMO-LUMO, NMR, UV, infrared intensities and Raman intensities are reported. The calculated first hyperpolarizability is comparable with the reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in good agreement with the values of similar structures. PMID:24915766
The actual content of quantum theoretical kinematics and mechanics
NASA Technical Reports Server (NTRS)
Heisenberg, W.
First, exact definitions are supplied for the terms: position, velocity, energy, etc. (of the electron, for instance), such that they are valid also in quantum mechanics. Canonically conjugated variables are determined simultaneously only with a characteristic uncertainty. This uncertainty is the intrinsic reason for the occurrence of statistical relations in quantum mechanics. Mathematical formulation is made possible by the Dirac-Jordan theory. Beginning from the basic principles thus obtained, macroscopic processes are understood from the viewpoint of quantum mechanics. Several imaginary experiments are discussed to elucidate the theory.
Theoretical calculations, far-infrared spectra and the potential energy surfaces of four cyclic silanes
NASA Astrophysics Data System (ADS)
Chun, Hye Jin; Colegrove, Lloyd F.; Laane, Jaan
Theoretical computations have been carried out to calculate the potential energy functions for the out-of-plane vibrations of four cyclic silanes, and the results were compared to experimental functions determined from far-infrared data. The experimental and computed ring-puckering potential functions for 1-silacyclopent-3-ene, which are in excellent agreement, are quartic in nature with tiny barriers to planarity. Similarly, the calculated and experimental potential functions for 1,3-disilacyclopent-3-ene are nearly identical. For silacyclopentane and 1,3-disilacyclopentane the calculations predict ring-twisitng barriers of 2493 cm-1 (vs. 2110 cm-1 observed) and 1395 cm-1, respectively. The conformational energies for the bent forms were calculated to be 1467 cm-1 (vs. 1509 cm-1 observed) for the former and 878 cm-1 for the latter relative to the energy of the twist minima. One-dimensional hindered pseudorotational potential energy functions were found to work well for predicting the observed far-infrared spectra for the bending (pseudorotational) vibration.
Uncertainties Associated with Theoretically Calculated N2-Broadened Half-Widths of H2O Lines
NASA Technical Reports Server (NTRS)
Ma, Q.; Tipping, R. H.; Gamache, R. R.
With different choices of the cut-offs used in theoretical calculations, we have carried out extensive numerical calculations of the N2-broadend Lorentzian half-widths of the H2O lines using the modified Robert-Bonamy formalism. Based on these results, we are able to thoroughly check for convergence. We find that, with the low-order cut-offs commonly used in the literature, one is able to obtain converged values only for lines with large half-widths. Conversely, for lines with small half-widths, much higher cut-offs are necessary to guarantee convergence. We also analyse the uncertainties associated with calculated half-widths, and these are correlated as above. In general, the smaller the half-widths, the poorer the convergence and the larger the uncertainty associated with them. For convenience, one can divide all H2O lines into three categories, large, intermediate, and small, according to their half-width values. One can use this division to judge whether the calculated half-widths are converged or not, based on the cut-offs used, and also to estimate how large their uncertainties are. We conclude that with the current Robert- Bonamy formalism, for lines in category lone can achieve the accuracy requirement set by HITRAN, whereas for lines in category 3, it 'is impossible to meet this goal.
Constant chemical potential approach for quantum chemical calculations in electrocatalysis
Schneider, Wolfgang B
Summary In order to simulate electrochemical reactions in the framework of quantum chemical methods, density functional theory, methods can be devised that explicitly include the electrochemical potential. In this work we discuss a Grand Canonical approach in the framework of density functional theory in which fractional numbers of electrons are used to represent an open system in contact with an electrode at a given electrochemical potential. The computational shortcomings and the additional effort in such calculations are discussed. An ansatz for a SCF procedure is presented, which can be applied routinely and only marginally increases the computational effort of standard constant electron number approaches. In combination with the common implicit solvent models this scheme can become a powerful tool, especially for the investigation of omnipresent non-faradaic effects in electrochemistry. PMID:24991504
Synthesis, characterization, optical properties and theoretical calculations of 6-fluoro coumarin
NASA Astrophysics Data System (ADS)
Bai, Yihui; Du, Jinyan; Weng, Xuexiang
6-Fluoro coumarin is synthesized and characterized by 1H NMR and 13C NMR. The optical properties of the title compound are investigated by UV-vis absorption and fluorescence emission spectra, the results show the title compound can absorb UV-vis light at 319, 269 and 215 nm, moreover it exhibits blue-purple fluorescence emission at 416 nm. Theoretical studies on molecular structure, infrared spectra (IR), nuclear magnetic resonance (1H NMR, 13C NMR) chemical shifts, UV-vis absorption and fluorescence emission of the synthesized compound have been worked out. Most chemical calculations were performed by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level (NMR at B3LYP/Aug-CC-Pvdz level) using Gaussian 09 program. The compared results reveal that the scaled theoretical vibrational frequencies are in good accordance with the observed spectra; computational chemical shifts are consistent with the experimental values in most parts, except for some minor deviations; the UV-vis absorption calculated matches the experimental one very well, and the fluorescence emission spectrum is in good agreement with the experimental one when the solute-solvent hydrogen-bonding interaction is considered. These good coincidences prove that the computational methods selected can be used to predict these properties of other similar materials where it is difficult to arrive at experimental results.
Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.
Ding, Yuanqing; Li, Xing-Cong; Ferreira, Daneel
Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (2). It identified the roles of the (2S)-flavanone and (aS)-HHDP moieties in generating the ECD spectrum of 2 and provided theoretical evidence for the empirical ECD rules applicable to monomeric flavanones and HHDP-containing compounds. The experimentally observed high-amplitude positive Cotton effect (CE) around 240 nm in 2 is derived from the (aS)-HHDP chromophore, while the low-amplitude negative CE in the 260-300 nm region is contributed by both the (aS)-HHDP and (2S)-flavanone moieties. The "linker" glucosyl moiety has little effect on the overall ECD. It appears that the respective chromophores in 2 contribute additively to the overall ECD, and the empirical rules are applicable for configurational assignment. However, if an (aR)-HHDP chromophore is present, as shown in mattucinol-7-O-[4'',6''-O-(aR)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (3), the dominant role of the (aR)-HHDP and interaction between the (aR)-HHDP and (2S)-flavanone moieties in its overall ECD may be confusing when applying the empirical rules to experimental ECD interpretation. Thus, theoretical calculation of the ECD that quantifies the contributions and interactions of different chromophores is essential for the assignment of the absolute configuration of such molecules. PMID:19099470
Thermochemical properties and contribution groups for ketene dimers and related structures from theoretical calculations.
Morales, Giovanni; MartĒnez, Ramiro
This research's main goals were to analyze ketene dimers' relative stability and expand group additivity value (GAV) methodology for estimating the thermochemical properties of high-weight ketene polymers (up to tetramers). The CBS-Q multilevel procedure and statistical thermodynamics were used for calculating the thermochemical properties of 20 cyclic structures, such as diketenes, cyclobutane-1,3-diones, cyclobut-2-enones and pyran-4-ones, as well as 57 acyclic base compounds organized into five groups. According to theoretical heat of formation predictions, diketene was found to be thermodynamically favored over cyclobutane-1,3-dione and its enol-tautomeric form (3-hydroxycyclobut-2-enone). This result did not agree with old combustion experiments. 3-Hydroxycyclobut-2-enone was found to be the least stable dimer and its reported experimental detection in solution may have been due to solvent effects. Substituted diketenes had lower stability than substituted cyclobutane-1,3-diones with an increased number of methyl substituents, suggesting that cyclobutane-1,3-dione type dimers are the major products because of thermodynamic control of alkylketene dimerization. Missing GAVs for the ketene dimers and related structures were calculated through linear regression on the 57 acyclic base compounds. Corrections for non next neighbor interactions (such as gauche, eclipses, and internal hydrogen bond) were needed for obtaining a highly accurate and precise regression model. To the best of our knowledge, the hydrogen bond correction for GAV methodology is the first reported in the literature; this correction was correlated to MP2/6-31Gdagger and HF/6-31Gdagger derived geometries to facilitate its application. GAVs assessed by the linear regression model were able to reproduce acyclic compounds' theoretical thermochemical properties and experimental heat of formation for acetylacetone. Ring formation and substituent position corrections were calculated by consecutively replacing the GAVs regarding the 20 cyclic structures' thermochemical properties. PMID:19572711
Can category-theoretic semantics resolve the problem of the interpretation of the quantum state vector?
Arkady Bolotin
Do correctness and completeness of quantum mechanics jointly imply that quantum state vectors are necessarily in one-to-one correspondence with elements of the physical reality? In terms of category theory, such a correspondence would stand for an isomorphism, so the problem of the status of the quantum state vector could be turned into the question of whether state vectors are necessarily isomorphic to elements of the reality. As it is argued in the present paper, in order to tackle this question, one needs to complement the category-theoretic approach to quantum mechanics with the computational-complexity-theoretic considerations. Based on such considerations, it is demonstrated in the paper that the hypothesis of the isomorphism existing between state vectors and elements of the reality is expected to be unsuitable for a generic quantum system.
Vibrational spectra, theoretical calculations, and two-dimensional potential energy surface for the ring-puckering vibrations of 2,4,7-trioxa[3.3.0]octane.
Chun, Hye Jin; Meinander, Niklas; Villarreal, John R; Laane, Jaan
2,4,7-Trioxa[3.3.0]octane (247TOO) is an unusual bicyclic molecule which can exist in four different conformational forms which are determined by the directions of the two ring- puckering motions. The vibrational assignments of 247TOO have been made based on its infrared and Raman spectra and theoretical density functional theory (DFT) calculations. The two ring-puckering motions (in-phase and out-of-phase) were observed in the Raman spectra of the liquid at 249 and 205 cm(-1) and these values correspond well to the DFT values of 247 and 198 cm(-1). Ab initio calculations were utilized to calculate the structures and conformational energies for the four energy minima and the barriers to interconversion and the data was utilized to generate a two-dimensional potential energy surface (PES) for the two ring-puckering motions. The resulting quantum state energies for this PES were then calculated in order to better understand the patterns that are produced when the PES has four energy minima at different energy values. The wave functions corresponding to the different quantum states were also calculated. The NMR spectrum of 247TOO showed the presence of the two lowest energy conformations, consistent with the results of the ab initio calculations. PMID:25514365
An experimental and theoretical study of L-tryptophan in an aqueous solution, combining two-layered ONIOM and SCRF calculations
NASA Astrophysics Data System (ADS)
Leyton, Patricio; Brunet, Juan; Silva, Viviana; Paipa, Carolina; Castillo, MarĒa Victoria; Brandßn, Silvia Antonia
ONIOM and SCRF calculations were performed to study the most stable theoretical structure of L-tryptophan in an aqueous solution phase and to observe the changes occurring in the structural and vibrational properties of L-tryptophan in the aqueous media. L-Tryptophan was characterized by infrared and Raman spectroscopies in the solid state and as an aqueous solution. Optimized geometries and relative stabilities for the L-tryptophan zwitterion were calculated while taking into account solvent effects using the self-consistent reaction field (SCRF) theory. The obtained results in the aqueous solution were compared with those calculated for the zwitterion in the gas phase by means of two-layered ONIOM calculations. For the complete assignments of the IR and Raman spectra of L-tryptophan in the aqueous solution phase, density functional theory (DFT) calculations were combined with Pulay's scaled quantum mechanical force field (SQMFF) methodology in order to fit the theoretical wavenumber values to the experimental values. Additionally, the roles of specific and bulk contributions from solvent effects on the properties of L-tryptophan were analyzed. Furthermore, bands corresponding to the normal modes of vibration were localized and assigned, and they served as the bases for the calculations of the corresponding force constants. Significant effects on the geometrical and vibrational frequencies were found for the studied zwitterion.
Quantum Monte Carlo calculations of NiO
NASA Astrophysics Data System (ADS)
Maezono, Ryo; Towler, Mike D.; Needs, Richard. J.
We describe variational and diffusion quantum Monte Carlo (VMC and DMC) calculations [1] of NiO using a 1024-electron simulation cell. We have used a smooth, norm-conserving, Dirac-Fock pseudopotential [2] in our work. Our trial wave functions were of Slater-Jastrow form, containing orbitals generated in Gaussian-basis UHF periodic calculations. Jastrow factor is optimized using variance minimization with optimized cutoff lengths using the same scheme as our previous work. [4] We apply the lattice regulated scheme [5] to evaluate non-local pseudopotentials in DMC and find the scheme improves the smoothness of the energy-volume curve. [1] CASINO ver.2.1 User Manual, University of Cambridge (2007). [2] J.R. Trail et.al., J. Chem. Phys. 122, 014112 (2005). [3] CRYSTAL98 User's Manual, University of Torino (1998). [4] Ryo Maezono et.al., Phys. Rev. Lett., 98, 025701 (2007). [5] Michele Casula, Phys. Rev. B 74, 161102R (2006).
Theoretical discussion for quantum computation in biological systems
NASA Astrophysics Data System (ADS)
Baer, Wolfgang
Analysis of the brain as a physical system, that has the capacity of generating a display of every day observed experiences and contains some knowledge of the physical reality which stimulates those experiences, suggests the brain executes a self-measurement process described by quantum theory. Assuming physical reality is a universe of interacting self-measurement loops, we present a model of space as a field of cells executing such self-measurement activities. Empty space is the observable associated with the measurement of this field when the mass and charge density defining the material aspect of the cells satisfy the least action principle. Content is the observable associated with the measurement of the quantum wave function ? interpreted as mass-charge displacements. The illusion of space and its content incorporated into cognitive biological systems is evidence of self-measurement activity that can be associated with quantum operations.
Quantum cognition: a new theoretical approach to psychology.
Bruza, Peter D; Wang, Zheng; Busemeyer, Jerome R
What type of probability theory best describes the way humans make judgments under uncertainty and decisions under conflict? Although rational models of cognition have become prominent and have achieved much success, they adhere to the laws of classical probability theory despite the fact that human reasoning does not always conform to these laws. For this reason we have seen the recent emergence of models based on an alternative probabilistic framework drawn from quantum theory. These quantum models show promise in addressing cognitive phenomena that have proven recalcitrant to modeling by means of classical probability theory. This review compares and contrasts probabilistic models based on Bayesian or classical versus quantum principles, and highlights the advantages and disadvantages of each approach. PMID:26058709
Theoretical model and numerical calculations for a quasi-one-dimensional organic ferromagnet
NASA Astrophysics Data System (ADS)
Fang, Z.; Liu, Z. L.; Yao, K. L.
A theoretical model is proposed to describe the quasi-one-dimensional organic ferromagnet polyBIPO. Different from Ovchinnikov's model, we consider the itineracy of ? electrons, the strong electron-phonon interaction, and electron-electron correlation in a one-dimensional system. Within the mean-field theory and Hartree approximation, allowing for full lattice relaxation, a set of self-consistent iterative equations is established to study the effects of ? electrons on the ferromagnetic order in the organic materials. The results of our calculations show that the ground state of the system is a stable ferromagnetic state. In the ferromagnetic ground state, the energy levels of the ? electrons will split off with respect to different spins. However, owing to the Peierls distortion of the lattice, all of the ? electrons will form an antiferromagnetic spin-density-wave chain.
Electron-Ion Recombination of Fe12 + Forming Fe11 +: Laboratory Measurements and Theoretical Calculations
NASA Astrophysics Data System (ADS)
Hahn, M.; Badnell, N. R.; Grieser, M.; Krantz, C.; Lestinsky, M.; M³ller, A.; Novotn², O.; Repnow, R.; Schippers, S.; Wolf, A.; Savin, D. W.
We have measured dielectronic recombination (DR) for Fe12 + forming Fe11 + using the heavy ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using our results, we have calculated a plasma rate coefficient from these data that can be used for modeling astrophysical and laboratory plasmas. For the low temperatures characteristic of photoionized plasmas, the experimentally derived rate coefficient is orders of magnitude larger than the previously recommended atomic data. The existing atomic data were also about 40% smaller than our measurements at temperatures relevant for collisionally ionized plasmas. Recent state-of-the-art theory has difficulty reproducing the detailed energy dependence of the DR spectrum. However, for the Maxwellian plasma rate coefficient, recent theoretical results agree with our measurements to within about 30% for both photoionized and collisionally ionized plasmas.
SPACON - A Theoretical Model for Calculating the Heat Transport Properties in Sphere-Pac Fuel Pins
Botta, F.; Hellwig, C. [Paul Scherrer Institute (Switzerland)
Nuclear fuel can be fabricated and used in the form of microspheres (sphere-pac fuel). The heat transport mechanisms in fuel pins containing sphere-pac fuel are however very different from those in pellet pins. They are controlled not only by the thermal conductivity of fuel, cladding, and fill gas but also by particle sizes and packing density, by their state of sintering, and by radiation and gas pressure. A theoretical model is presented accounting for all these parameters, but still simple and fast enough to be implemented into a fuel pin modeling code. The basic geometrical element for this model is derived from the orthorhombic packing. For calculation of a binary package, four different radial zones within the basic element are distinguished, i.e., neck zone, gas zone, infiltrated zone, and bypass zone. The method presented here combines an analytical one-dimensional treatment with a radial heat flow relaxation procedure simulating the second (radial) dimension. Results are compared with experimental and theoretical data from the literature. With the model presented here, sophisticated modeling of sphere-pac fuel pins is possible.
Conformations of silica-bound (pentafluorophenyl)propyl groups determined by solid-state NMR spectroscopy and theoretical calculations.
Mao, Kanmi; Kobayashi, Takeshi; Wiench, Jerzy W; Chen, Hung-Ting; Tsai, Chih-Hsiang; Lin, Victor S-Y; Pruski, Marek
The conformations of (pentafluorophenyl)propyl groups (-CH(2)-CH(2)-CH(2)-C(6)F(5), abbreviated as PFP), covalently bound to the surface of mesoporous silica nanoparticles (MSNs), were determined by solid-state NMR spectroscopy and further refined by theoretical modeling. Two types of PFP groups were described, including molecules in the prone position with the perfluorinated aromatic rings located above the siloxane bridges (PFP-p) and the PFP groups denoted as upright (PFP-u), whose aromatic rings do not interact with the silica surface. Two-dimensional (2D) (13)C-(1)H, (13)C-(19)F and (19)F-(29)Si heteronuclear correlation (HETCOR) spectra were obtained with high sensitivity on natural abundance samples using fast magic angle spinning (MAS), indirect detection of low-gamma nuclei and signal enhancement by Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence. 2D double-quantum (DQ) (19)F MAS NMR spectra and spin-echo measurements provided additional information about the structure and mobility of the pentafluorophenyl rings. Optimization of the PFP geometry, as well as calculations of the interaction energies and (19)F chemical shifts, proved very useful in refining the structural features of PFP-p and PFP-u functional groups on the silica surface. The prospects of using the PFP-functionalized surface to modify its properties (e.g., the interaction with solvents, especially water) and design new types of the heterogeneous catalytic system are discussed. PMID:20707348
Rationalization and Design of Enhanced Photoinduced Cycloreversion in Photochromic Dimethyldihydropyrenes by Theoretical Calculations.
Boggio-Pasqua, Martial; Garavelli, Marco
This study presents a computational investigation of the initial step of the dimethyldihydropyrene (DHP) to cyclophanediene (CPD) photoinduced ring-opening reaction using time-dependent density functional theory (TD-DFT). In particular, the photochemical path corresponding to the formation of the CPD precursor (CPD*) on the zwitterionic state is scrutinized. The TD-DFT approach was first validated on the parent compound against accurate ab initio calculations. It confirms that CPD* formation is efficiently quenched in this system by an easily accessible S2/S1 conical intersection located in the vicinity of the CPD* minimum and leading to a locally excited state minimum responsible for DHP luminescence. Increased ring-opening quantum yields were observed in benzo[e]-fused-DHP (DHP-1), isobutenyl-DHP (DHP-2), and naphthoyl-DHP (DHP-3). The calculations show that CPD* formation is much more favorable in these systems, either due to an inversion of electronic states in DHP-1, suppressing the formation of the locally excited state, or due to efficient stabilization of CPD* on the S1 potential energy surface in DHP-2 and DHP-3. Both effects can be combined in a rationally designed benzo[e]-fused-naphthoyl-DHP (DHP-4) for which we anticipate an unprecedented efficiency. PMID:25582806
Number-Theoretic Nature of Communication in Quantum Spin Systems
NASA Astrophysics Data System (ADS)
Godsil, Chris; Kirkland, Stephen; Severini, Simone; Smith, Jamie
The last decade has witnessed substantial interest in protocols for transferring information on networks of quantum mechanical objects. A variety of control methods and network topologies have been proposed, on the basis that transfer with perfect fidelityŚi.e., deterministic and without information lossŚis impossible through unmodulated spin chains with more than a few particles. Solving the original problem formulated by Bose [Phys. Rev. Lett. 91, 207901 (2003)], we determine the exact number of qubits in unmodulated chains (with an XY Hamiltonian) that permit transfer with a fidelity arbitrarily close to 1, a phenomenon called pretty good state transfer. We prove that this happens if and only if the number of nodes is n=p-1, 2p-1, where p is a prime, or n=2m-1. The result highlights the potential of quantum spin system dynamics for reinterpreting questions about the arithmetic structure of integers and, in this case, primality.
A quantum theoretical approach to information processing in neural networks
NASA Astrophysics Data System (ADS)
Barahona da Fonseca, Josķ; Barahona da Fonseca, Isabel; Suarez Araujo, Carmen Paz; Sim§es da Fonseca, Josķ
A reinterpretation of experimental data on learning was used to formulate a law on data acquisition similar to the Hamiltonian of a mechanical system. A matrix of costs in decision making specifies values attributable to a barrier that opposed to hypothesis formation about decision making. The interpretation of the encoding costs as frequencies of oscillatory phenomena leads to a quantum paradigm based in the models of photoelectric effect as well as of a particle against a potential barrier. Cognitive processes are envisaged as complex phenomena represented by structures linked by valence bounds. This metaphor is used to find some prerequisites to certain types of conscious experience as well as to find an explanation for some pathological distortions of cognitive operations as they are represented in the context of the isolobal model. Those quantum phenomena are understood as representing an analogue programming for specific special purpose computations. The formation of complex chemical structures within the context of isolobal theory is understood as an analog quantum paradigm for complex cognitive computations.
Theoretical approach of the electroluminescence quenching in (polymer-CdSe quantum dot) nanocomposite
NASA Astrophysics Data System (ADS)
Mastour, N.; Mejatty, M.; Bouchriha, H.
A theoretical approach based on the rate equation of exciton density for the electroluminescence quenching in (polymers-quantum dots) nanocomposite is developed. It is shown that the light intensity observed in the nanocomposite depends respectively on the quantum dots concentration, the injected charge carriers, the exciton density, and the F÷rster energy transfer between polymer and quantum dots. We have found that the significant reduction of the light intensity is related to the exciton density profiles which exhibit a monotonic decrease with the increase of F÷rster transfer mechanism. Our theoretical approach for the electroluminescence agrees with experimental results observed in hybrid structure (MEH-PPV) with CdSe quantum dots. The maximum of exciton density is also estimated and we have obtained a value for the exciton diffusion length of 10 nm which is consistent with the available experimental results.
The rigorous stochastic matrix multiplication scheme for the calculations of reduced equilibrium density matrices of open multilevel quantum systems
Chen, Xin, E-mail: email@example.com [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
Understanding the roles of the temporary and spatial structures of quantum functional noise in open multilevel quantum molecular systems attracts a lot of theoretical interests. I want to establish a rigorous and general framework for functional quantum noises from the constructive and computational perspectives, i.e., how to generate the random trajectories to reproduce the kernel and path ordering of the influence functional with effective Monte Carlo methods for arbitrary spectral densities. This construction approach aims to unify the existing stochastic models to rigorously describe the temporary and spatial structure of Gaussian quantum noises. In this paper, I review the Euclidean imaginary time influence functional and propose the stochastic matrix multiplication scheme to calculate reduced equilibrium density matrices (REDM). In addition, I review and discuss the Feynman-Vernon influence functional according to the Gaussian quadratic integral, particularly its imaginary part which is critical to the rigorous description of the quantum detailed balance. As a result, I establish the conditions under which the influence functional can be interpreted as the average of exponential functional operator over real-valued Gaussian processes for open multilevel quantum systems. I also show the difference between the local and nonlocal phonons within this framework. With the stochastic matrix multiplication scheme, I compare the normalized REDM with the Boltzmann equilibrium distribution for open multilevel quantum systems.
A quantum Monte Carlo calculation of the ground state energy of the hydrogen molecule
Anderson, James B.
A quantum Monte Carlo calculation of the ground state energy of the hydrogen molecule Carol A of the hydrogen molecule using the quantum Monte Carlo (QMC) method of solving the Schrodinger equation, without protons). Two different methods were employed: the diffusion quantum Monte Carlo (DQMC) method
Theoretical calculating the thermodynamic properties of solid sorbents for CO{sub 2} capture applications
Duan, Yuhua
Since current technologies for capturing CO{sub 2} to fight global climate change are still too energy intensive, there is a critical need for development of new materials that can capture CO{sub 2} reversibly with acceptable energy costs. Accordingly, solid sorbents have been proposed to be used for CO{sub 2} capture applications through a reversible chemical transformation. By combining thermodynamic database mining with first principles density functional theory and phonon lattice dynamics calculations, a theoretical screening methodology to identify the most promising CO{sub 2} sorbent candidates from the vast array of possible solid materials has been proposed and validated. The calculated thermodynamic properties of different classes of solid materials versus temperature and pressure changes were further used to evaluate the equilibrium properties for the CO{sub 2} adsorption/desorption cycles. According to the requirements imposed by the pre- and post- combustion technologies and based on our calculated thermodynamic properties for the CO{sub 2} capture reactions by the solids of interest, we were able to screen only those solid materials for which lower capture energy costs are expected at the desired pressure and temperature conditions. Only those selected CO{sub 2} sorbent candidates were further considered for experimental validations. The ab initio thermodynamic technique has the advantage of identifying thermodynamic properties of CO{sub 2} capture reactions without any experimental input beyond crystallographic structural information of the solid phases involved. Such methodology not only can be used to search for good candidates from existing database of solid materials, but also can provide some guidelines for synthesis new materials. In this presentation, we first introduce our screening methodology and the results on a testing set of solids with known thermodynamic properties to validate our methodology. Then, by applying our computational method to several different kinds of solid systems, we demonstrate that our methodology can predict the useful information to help developing CO{sub 2} capture Technologies.
Hyperon puzzle: hints from quantum Monte Carlo calculations.
Lonardoni, Diego; Lovato, Alessandro; Gandolfi, Stefano; Pederiva, Francesco
The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and ? particles by using the auxiliary field diffusion MonteĀCarlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars. PMID:25793808
Molecular Electrical Properties from Quantum Monte Carlo Calculations: Application to Ethyne
Guidoni, Leonardo
Molecular Electrical Properties from Quantum Monte Carlo Calculations: Application to Ethyne values and in very good agreement with experimental data and with other quantum chemistry calculations The correct modeling of the electrostatic and dispersive interactions in atomic and molecular systems requires
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms.
Song, Lei; Balakrishnan, N; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15?000 cm(-1) based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models. PMID:26026443
Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms
NASA Astrophysics Data System (ADS)
Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.
We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 - 30 to v' = 0, j' are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm-1 based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ? 3 to v' = 0, j' are reported for the first time at this level of theory. Also calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H-CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H-CO collisions in astrophysical models.
Theoretical calculations of nonlinear refraction and absorption coefficients of doped graphene
NASA Astrophysics Data System (ADS)
Margulis, Vl A.; Muryumin, E. E.; Gaiduk, E. A.
In this study, we present the first theoretical predictions concerning the nonlinear refractive and absorptive properties of the doped graphene in which the Fermi energy {{E}F} of charge carriers (noninteracting massless Dirac fermions) is controlled by an external gate voltage. We base our study on the original perturbation theory technique developed by Genkin and Mednis (1968 Sov. Phys. JETP 27 609) for calculating the nonlinear-optical (NLO) response coefficients of bulk crystalline semiconductors with partially filled bands. Using a simple tight-binding model for the ?-electron energy bands of graphene, we obtain analytic expressions for the nonlinear refractive index {{n}2}(? ) and the nonlinear absorption coefficient {{? }2}(? ) of the doped graphene at photon energies above twice the value of the Fermi energy (\\hbar ? \\gt 2{{E}F}). We show that in this spectral region, both the nonlinear refraction ant the nonlinear absorption are determined predominantly by the combined processes which simultaneously involve intraband and interband motion of ?-electrons. Our calculations indicate that extremely large negative values of n2 (of the order of -{{10}-6} cm2 W?1) can be achieved in the graphene at a relatively low doping level (of about 1012 cm?2) provided that the excitation frequency slightly exceeds the threshold frequency corresponding to the onset of interband transitions. With a further increase of the radiation frequency, the {{n}2}(? ) becomes positive and begins to decrease in its absolute magnitude. The peculiar frequency dispersion of n2 and a negative sign of the {{? }2} (absorption bleaching), as predicted by our theory, suggest that the doped graphene is a prospective NLO material to be used in practical optical switching applications.
Theoretical analysis of diffused quantum-well lasers and optical amplifiers
Wallace C. H. Choy; K. S. Chan
Diffused quantum-well (QW) distributed feedback (DFB) lasers and optical amplifiers will be theoretically analyzed in this paper. For DFB lasers, a design rule will be proposed and the validity of the design rule will be discussed with respect to changes in the injected carrier density. The range of grating period, which can be used in the design, is discussed. As
Advanced Quantum Mechanical Calculation of Superheavy Ions: Energy Levels, Radiation and Finite Nuclear Size Effects
Glushkov, Alexander V.; Gurnitskaya, E.P.; Loboda, A.V. [Nucl.-Laser Spectroscopy Centre, Odessa University, P.O.Box 24a, Odessa-9, 65009 (Ukraine); Inst. Applied Mathematics, Odessa University, P.O.Box 24a, Odessa-9, 65009 (Ukraine)
Advanced quantum approach to calculation of spectra for superheavy ions with an account of relativistic, correlation, nuclear, radiative effects is developed and based on the gauge invariant quantum electrodynamics (QED) perturbation theory (PT). The Lamb shift polarization part is calculated in the Ueling approximation, self-energy part is defined within a new non-PT procedure of Ivanov-Ivanova. Calculation results for energy levels, hyperfine structure parameters of some heavy elements ions are presented.
Supercomputer requirements for theoretical chemistry
Walker, R.B.; Hay, P.J.; Galbraith, H.W.
Many problems important to the theoretical chemist would, if implemented in their full complexity, strain the capabilities of today's most powerful computers. Several such problems are now being implemented on the CRAY-1 computer at Los Alamos. Examples of these problems are taken from the fields of molecular electronic structure calculations, quantum reactive scattering calculations, and quantum optics. 12 figures.
Molecular structure and nicotinic activity of arecoline. A gas electron diffraction study combined with theoretical calculations
NASA Astrophysics Data System (ADS)
Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro
The molecular structure of arecoline (methyl 1,2,5,6-tetrahydro-1-methylnicotinate, ? has been determined by gas electron diffraction. Diffraction patterns were taken at about 370 K. Structural constraints for the data analysis were obtained from MP2/6-31G** calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the force constants obtained from the gas-phase vibrational frequencies and the B3LYP/6-31G** calculations. The electron diffraction data were well reproduced by assuming the mixture of four conformers. The determined structural parameters ( rg (┼) and ? (░)) for the main conformer with 3 ? in parentheses are as follows: < rg(N-C ring)>=1.456(4); rg(N-C methyl)=1.451 (d.p.); rg(C dbnd6 C)=1.339(9); < rg(C-C)>=1.512(3); rg(O-C methyl)=1.434(5); rg(C(O)-O)=1.355 (d.p.); rg(C dbnd6 O)=1.209(4); the out-of-plane angle of the methyl group=50.3(23); ?C ringN ringC ring=112.8(30); ?N ringC ringC ring(H 2)=110.5(16); =118.4(5); ?C dbnd6 CC(O)=116.8(7); ?CC dbnd6 O=127.6(9); ?CC-O=109.8(8), where the angle brackets denote averaged values and d.p. denotes dependent parameters. Fixing the abundances of the minor conformers, Ax-s- cis and Ax-s- trans, at the theoretical values (13% in total), those of the Eq-s- cis and Eq-s- trans conformers were determined to be 46(16) and 41(16)%, respectively. Here Ax and Eq denote the axial and equatorial directions of the N-CH 3 bond and s- cis and s- trans show the orientation of the methoxycarbonyl group expressed by the configuration of the C dbnd6 O and C dbnd6 C bonds. The N⋯O carbonyl distances of the Eq-s- cis and Ax-s- cis conformers are 4.832(13) and 4.874(16) ┼, respectively. They are close to the N⋯N distance of the most abundant conformer of nicotine, 4.885(6) ┼, suggesting that the Eq-s- cis and Ax-s- cis conformers have nicotinic activity.
Theoretical gain of strained GeSn0.02/Ge1-x-y'SixSny' quantum well laser
NASA Astrophysics Data System (ADS)
Zhu, Yuan-Hui; Xu, Qiang; Fan, Wei-Jun; Wang, Jian-Wei
Using effective-mass Hamiltonian model of semiconductors quantum well structures, we investigate the electronic structures of the ?-conduction and L-conduction subbands of GeSn/GeSiSn strained quantum well structure with an arbitrary composition. Our theoretical model suggests that the band structure could be widely modified to be type I, negative-gap or indirect-gap type II quantum well by changing the mole fraction of ?-Sn and Si in the well and barrier layers, respectively. The optical gain spectrum in the type I quantum well system is calculated, taking into account the electrons leakage from the ?-valley to L-valley of the conduction band. We found that by increasing the mole fraction of ?-Sn in the barrier layer and not in the well layer, an increase in the tensile strain effect can significantly enhance the transition probability, and a decrease in Si composition in the barrier layer, which lowers the band edge of ?-conduction subbands, also comes to a larger optical gain.
Theoretical calculation of the angular distribution of radiation at the output of a flat nanodimensional X-ray waveguide
NASA Astrophysics Data System (ADS)
Lerer, A. M.; Mazuritskii, M. I.; Makhno, P. V.; Noranovich, D. A.
A model is proposed for theoretical calculations of the angular distribution of radiation intensity at the output of a flat X-ray waveguide representing an air-filled gap between two quartz plates. Good agreement between the theoretical and experimental angular profiles of CuK? fluorescence intensity is obtained for planar waveguides with the gap widths ranging from 40 to 3000 nm. It is concluded that the Kirchhoff method can be applied to calculations of the spatial distribution of radiation intensity at the X-ray waveguide output.
Entanglement as Measure of Electron-Electron Correlation in Quantum Chemistry Calculations
Zhen Huang; Sabre Kais
In quantum chemistry calculations, the correlation energy is defined as the difference between the Hartree-Fock limit energy and the exact solution of the nonrelativistic Schrodinger equation. With this definition, the electron correlation effects are not directly observable. In this report, we show that the entanglement can be used as an alternative measure of the electron correlation in quantum chemistry calculations. Entanglement is directly observable and it is one of the most striking properties of quantum mechanics. As an example we calculate the entanglement for He atom and H2 molecule with different basis sets.
Performance test of multicomponent quantum mechanical calculation with polarizable continuum model for proton chemical shift.
Kanematsu, Yusuke; Tachikawa, Masanori
Multicomponent quantum mechanical (MC_QM) calculations with polarizable continuum model (PCM) have been tested against liquid (1)H NMR chemical shifts for a test set of 80 molecules. Improvement from conventional quantum mechanical calculations was achieved for MC_QM calculations. The advantage of the multicomponent scheme could be attributed to the geometrical change from the equilibrium geometry by the incorporation of the hydrogen nuclear quantum effect, while that of PCM can be attributed to the change of the electronic structure according to the polarization by solvent effects. PMID:25915075
Multiscale analytic calculation of valley splitting in silicon quantum wells.
NASA Astrophysics Data System (ADS)
Chutia, Sucismita; Coppersmith, Susan; Friesen, Mark
Valley splitting in Si/SiGe quantum wells is a central issue for Si based quantum dot quantum computers. The valley coupling arises due to the mixing of states at a sharp quantum well interface. The effective mass theory provides an essential tool for studying the valley splitting in various geometries. However, the magnitude of the splitting must still be determined microscopically, e.g., from atomistic theories. Here, we develop a multiscale theory that bridges the effective mass and atomistic approaches. Since the valley coupling occurs within just a few atomic layers of the interface, we splice a tight binding treatment of the interface into an effective mass treatment of the extended wavefunction. This multiscale theory yields analytical solutions for the valley splitting with no adjustable parameters.
Multi-million atom electronic structure calculations for quantum dots
Muhammad Usman
Quantum dots grown by self-assembly process are typically constructed by 50,000 to 5,000,000 structural atoms which confine a small, countable number of extra electrons or holes in a space that is comparable in size to the electron wavelength. Under such conditions quantum dots can be interpreted as artificial atoms with the potential to be custom tailored to new functionality. In
A pedagogical introduction to quantum integrability, with a view towards theoretical high-energy physics
J. Lamers
These are lecture notes of an introduction to quantum integrability given at the Tenth Modave Summer School in Mathematical Physics, 2014, aimed at PhD candidates and junior researchers in theoretical physics. We introduce spin chains and discuss the coordinate Bethe ansatz (CBA) for a representative example: the Heisenberg XXZ model. The focus lies on the structure of the CBA and on its main results, deferring a detailed treatment of the CBA for the general $M$-particle sector of the XXZ model to an appendix. Subsequently the transfer-matrix method is discussed for the six-vertex model, uncovering a relation between that model and the XXZ spin chain. Equipped with this background the quantum inverse-scattering method (QISM) and algebraic Bethe ansatz (ABA) are treated. We emphasize the use of graphical notation for algebraic quantities as well as computations. Finally we turn to quantum integrability in the context of theoretical high-energy physics. We discuss factorized scattering in two-dimensional QFT, and conclude with a qualitative introduction to one current research topic relating quantum integrability to theoretical high-energy physics: the Bethe/gauge correspondence.
Quantum and conversion efficiency calculation of AlGaAs/GaAs multiple quantum well solar cells
NASA Astrophysics Data System (ADS)
Rimada, J. C.; Hernandez, L.; Connolly, J. P.; Barnham, K. W. J.
The quantum well solar cell (QWSC) is a novel device that has been proposed by Barnham and co-workers at Imperial College London. In this work, the quantum efficiency for AlGaAs/GaAs QWSC has been calculated and compared with available data from the group at Imperial College London. Quantum efficiency calculations will be presented and compared with experimental data for several AlGaAs/GaAs QWSC, obtaining good agreement. The photocurrent then is calculated from the quantum efficiency calculations and included in the J(V) relation to optimize the efficiency of AlGaAs/GaAs QWSC. It also shows that for a range of quantum well widths and barrier bandgaps the conversion efficiencies of the quantum well solar cell are higher than the corresponding homogeneous p-i-n solar cell. Our results give a broad representation of quantum well solar cell operation, and provide a profitable guide for designing and interpreting the performance characteristics of AlGaAs/GaAs QWSCs.
Theoretical ROVibrational Energies (TROVE): A robust numerical approach to the calculation of rovibrational energies for polyatomic molecules
Sergei N. Yurchenko; Walter Thiel; Per Jensen
We present a new computational method with associated computer program TROVE (Theoretical ROVibrational Energies) to perform variational calculations of rovibrational energies for general polyatomic molecules of arbitrary structure in isolated electronic states. The (approximate) nuclear kinetic energy operator is represented as an expansion in terms of internal coordinates. The main feature of the computational scheme is a numerical construction of
Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen broadened water vapor overtone transitions in the
Gamache, Robert R.
Diode laser spectroscopic measurements and theoretical calculations of line parameters of nitrogen region are measured by using a tunable diode laser spectrometer. Water vapor is kept at its saturated. in the presence of perturbers like oxygen, nitrogen, air, argon etc [11-13]. 3 #12;FTIR and diode laser
Exact quantum Monte Carlo calculations of the potential energy surface for the reaction H+H,-+H,+H
Anderson, James B.
Exact quantum Monte Carlo calculations of the potential energy surface for the reaction H" quantum Monte Carlo calculations of the potential energy surface for the reaction H+H2-+H2+H. The method of r0.2 kcal/mol. INTRODUCTION In a previous paper' we reported quantum Monte Carlo calculations
Theoretical modeling of multiple quantum well lasers with tunneling injection and tunneling transport between quantum wells
M. Kucharczyk; M. S. Wartak; P. Weetman; P.-K. Lau
Multiple quantum well lasers with tunneling transport of carriers represent a new class of semiconductor lasers. Tunneling can be utilized twofold: as an injection mechanism which drives electrons from a separate confinement heterostructure into active well and also as a mechanism facilitating transport between quantum wells. Since tunneling is normally a very fast process, one can expect that employing the
State-to-State Quantum Mechanical Calculations of Rate Coefficients + H2 HD + H+
Honvault, Pascal
of a time-independent quantum mechanical approach. Cross-sections and rate coefficients are calculated fractionation. It is worthwhile to mention that it is also one of the main sources of HD in interstellar clouds
Molecular structure analysis and spectroscopic characterization of carbimazole with experimental (FT-IR, FT-Raman and UV-Vis) techniques and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Gnanasambandan, T.; Gunasekaran, S.; Seshadri, S.
The complete vibrational assignment and analysis of the fundamental modes of carbimazole (CBZ) was carried out using the experimental FTIR, FT-Raman and UV-Vis data and quantum chemical studies. The observed vibrational data were compared with the wavenumbers derived theoretically for the optimized geometry of the compound from the DFT-B3LYP gradient calculations employing 6-31G(d,p) and 6-311++G(d,p) basis sets. Thermodynamic properties like entropy, heat capacity and enthalpy have been calculated for the molecule. HOMO-LUMO energy gap has been calculated. The intramolecular contacts have been interpreted using natural bond orbital (NBO) and natural localized molecular orbital (NLMO) analysis. Important non-linear properties such as electric dipole moment and first hyperpolarizability of CBZ have been computed using B3LYP quantum chemical calculation. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.
Quantum Wavepacket Ab-initio Molecular Dynamics Formalism for Calculating Electron Transport in Molecular Wires
Iyengar, Srinivasan S.
as a time-dependent quantum system interacting with the molecular wire device. We also make an assumptionQuantum Wavepacket Ab-initio Molecular Dynamics Formalism for Calculating Electron Transport in Molecular Wires Alexander B. Pacheco and Srinivasan S. Iyengar Department of Chemistry, Indiana University
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Kahn, L. R.
Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.
Quantum complex rotation and uniform semiclassical calculations of complex energy eigenvalues
J. N. L. Connor; A. D. Smith
Quantum and semiclassical calculations of complex energy eigenvalues have been carried out for an exponential potential of the form V0r2 exp(?r) and Lennard-Jones (12,6) potential. A straightforward method, based on the complex coordinate rotation technique, is described for the quantum calculation of complex eigenenergies. For singular potentials, the method involves an inward and outward integration of the radial Schro©dinger equation,
Quantum complex rotation and uniform semiclassical calculations of complex energy eigenvalues
J. N. L. Connor; A. D. Smith
Quantum and semiclassical calculations of complex energy eigenvalues have been carried out for an exponential potential of the form VŌr┬▓ exp(-r) and Lennard-Jones (12,6) potential. A straightforward method, based on the complex coordinate rotation technique, is described for the quantum calculation of complex eigenenergies. For singular potentials, the method involves an inward and outward integration of the radial Schroedinger equation,
Photophysics of graphene quantum dots: Insights from electronic structure calculations
Stefan Schumacher
Understanding electronic excitations in graphene nanostructures plays a crucial role in utilizing these recently emerging systems in optoelectronics and photonics. Based on time-dependent density functional theory, we elucidate on optical selection rules in isolated graphene quantum dots (QDs) and their relation to the system symmetry and bring the general results into a broader context with other semiconductor QD systems. The
A perspective on quantum mechanics calculations in ADMET predictions.
Bowen, J Phillip; G³ner, Osman F
Understanding the molecular basis of drug action has been an important objective for pharmaceutical scientists. With the increasing speed of computers and the implementation of quantum chemistry methodologies, pharmacodynamic and pharmacokinetic problems have become more computationally tractable. Historically the former has been the focus of drug design, but within the last two decades efforts to understand the latter have increased. It takes about fifteen years and over $1 billion dollars for a drug to go from laboratory hit, through lead optimization, to final approval by the U.S. Food and Drug Administration. While the costs have increased substantially, the overall clinical success rate for a compound to emerge from clinical trials is approximately 10%. Most of the attrition rate can be traced to ADMET (absorption, distribution, metabolism, excretion, and toxicity) problems, which is a powerful impetus to study these issues at an earlier stage in drug discovery. Quantum mechanics offers pharmaceutical scientists the opportunity to investigate pharmacokinetic problems at the molecular level prior to laboratory preparation and testing. This review will provide a perspective on the use of quantum mechanics or a combination of quantum mechanics coupled with other classical methods in the pharmacokinetic phase of drug discovery. A brief overview of the essential features of theory will be discussed, and a few carefully selected examples will be given to highlight the computational methods. PMID:23675934
Molecular structure of cotinine studied by gas electron diffraction combined with theoretical calculations
NASA Astrophysics Data System (ADS)
Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro
The molecular structure of cotinine (( S)-1-methyl-5-(3-pyridinyl)-2-pyrrolidinone), the major metabolite of nicotine, has been determined at about 182 ░C by gas electron diffraction combined with MP2 and DFT calculations. The diffraction data are consistent with the existence of the (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers, where ax and eq indicate the configuration of the pyrrolidinone ring by means of the position (axial and equatorial) of the pyridine ring, and sc, sp and ap distinguish the isomers arising from the internal rotation around the bond connecting the two rings. The (CH 3)NCCC(N) dihedral angles, ?, of the (ax, sc) and (eq, sp) conformers were determined independently to be 158(12)░ and 129(13)░, respectively, where the numbers in parentheses are three times the standard errors, 3 ?. According to the MP2 calculations, the corresponding dihedral angles for the (ax, ap) and (eq, ap) conformers were assumed to differ by 180░ from their syn counterparts. The ratios x(ax, sc)/ x(ax, ap) and x(eq, sp)/ x(eq, ap) were taken from the theoretically estimated free energy differences, ? G, where x is the abundance of the conformer. The resultant abundances of (ax, sc), (ax, ap), (eq, sp) and (eq, ap) conformers are 34(6)%, 21% (d.p.), 28% (d.p.), and 17% (d.p.), respectively, where d.p. represents dependent parameters. The determined structural parameters ( rg (┼) and ? ? (░)) of the most abundant conformer, (ax, sc), are as follows: r(N sbnd C) pyrrol = 1.463(5); r(N sbnd C methyl) = 1.457(?); r(N sbnd C( dbnd O)) = 1.384(12); r(C dbnd O) = 1.219(5); < r(C sbnd C) pyrrol> = 1.541(3); r(C pyrrolsbnd C pyrid) = 1.521(?); < r(C sbnd C) pyrid> = 1.396(2); < r(C sbnd N) pyrid> = 1.343(?); ?(CNC) pyrrol = 113.9(11); ?CCC pyrrol(-C pyrid) = 103.6(?); ?NCO = 124.1(13); ?NC pyrrolC pyrid = 113.1(12); ?C pyrrolC pyrrolC pyrid = 113.3(?); ?(CNC) pyrid = 117.1(2); (NCC) pyrid> = 124.4(?); ?C methylNC( dbnd O) = ?C methylNC(-C pyrid) = 122.8(d.p.); ?NC( dbnd O)C = 107.1(d.p.); ?NC pyrrol(-C pyrid)C pyrrol = 103.0(d.p.) and ?CCC( dbnd O) = 105.2(d.p.), where ? in the parentheses means that the parameter is bound to the preceding one and < > denote average values. The puckering angle, ?, of the pyrrolidinone ring is 26(3)░. The N⋯N distances of the (ax, sc) and (eq, sp) conformers, which are 4.844(5) and 4.740(5) ┼, respectively, are close to that of the most stable conformer of nicotine, 4.885(6) ┼ and the corresponding one of arecoline, 4.832(13) ┼. It is concluded that the weak nicotinic activity of cotinine cannot be ascribed to such a small difference in the N⋯N distances.
Information-theoretic security proof for quantum-key-distribution protocols
Renato Renner; Nicolas Gisin; Barbara Kraus
We present a technique for proving the security of quantum-key-distribution (QKD) protocols. It is based on direct information-theoretic arguments and thus also applies if no equivalent entanglement purification scheme can be found. Using this technique, we investigate a general class of QKD protocols with one-way classical post-processing. We show that, in order to analyze the full security of these protocols,
A theoretical analysis of the optical absorption properties in one-dimensional InAs/GaAs quantum dot superlattices
Kotani, Teruhisa, E-mail: email@example.com [Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567 (Japan); Institute for Nanoelectronics, Technische Universitõt M³nchen, Arcisstr. 21, 80333 Munich (Germany); Birner, Stefan [Institute for Nanoelectronics, Technische Universitõt M³nchen, Arcisstr. 21, 80333 Munich (Germany); Walter Schottky Institute, Technische Universitõt M³nchen, Am Coulombwall 4, 85748 Garching (Germany); Lugli, Paolo [Institute for Nanoelectronics, Technische Universitõt M³nchen, Arcisstr. 21, 80333 Munich (Germany); Hamaguchi, Chihiro [Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho, Tenri, Nara 632-8567 (Japan)
We present theoretical investigations of miniband structures and optical properties of InAs/GaAs one-dimensional quantum dot superlattices (1D-QDSLs). The calculation is based on the multi-band kĘp theory, including the conduction and valence band mixing effects, the strain effect, and the piezoelectric effect; all three effects have periodic boundary conditions. We find that both the electronic and optical properties of the 1D-QDSLs show unique states which are different from those of well known single quantum dots (QDs) or quantum wires. We predict that the optical absorption spectra of the 1D-QDSLs strongly depend on the inter-dot spacing because of the inter-dot carrier coupling and changing strain states, which strongly influence the conduction and valence band potentials. The inter-miniband transitions form the absorption bands. Those absorption bands can be tuned from almost continuous (closely stacked QD case) to spike-like shape (almost isolated QD case) by changing the inter-dot spacing. The polarization of the lowest absorption peak for the 1D-QDSLs changes from being parallel to the stacking direction to being perpendicular to the stacking direction as the inter-dot spacing increases. In the case of closely stacked QDs, in-plane anisotropy, especially [110] and [11{sup »}0] directions also depend on the inter-dot spacing. Our findings and predictions will provide an additional degree of freedom for the design of QD-based optoelectronic devices.
Theoretical Analysis About Quantum Noise Squeezing of Optical Fields From an Intracavity Frequency-Doubled Laser
NASA Technical Reports Server (NTRS)
Zhang, Kuanshou; Xie, Changde; Peng, Kunchi
The dependence of the quantum fluctuation of the output fundamental and second-harmonic waves upon cavity configuration has been numerically calculated for the intracavity frequency-doubled laser. The results might provide a direct reference for the design of squeezing system through the second-harmonic-generation.
Theoretical oxidation state analysis of Ru-(bpy)3: influence of water solvation and Hubbard correction in first-principles calculations.
Reeves, Kyle G; Kanai, Yosuke
Oxidation state is a powerful concept that is widely used in chemistry and materials physics, although the concept itself is arguably ill-defined quantum mechanically. In this work, we present impartial comparison of four, well-recognized theoretical approaches based on Lowdin atomic orbital projection, Bader decomposition, maximally localized Wannier function, and occupation matrix diagonalization, for assessing how well transition metal oxidation states can be characterized. Here, we study a representative molecular complex, tris(bipyridine)ruthenium. We also consider the influence of water solvation through first-principles molecular dynamics as well as the improved electronic structure description for strongly correlated d-electrons by including Hubbard correction in density functional theory calculations. PMID:25028017
Theoretical calculations of the temperature dependence of the electrical and thermal conductivities of liquid gallium
M. Sayem El-Daher; Richard D. Murphy
The electrical and thermal resistivities of liquid gallium are calculated over a range of temperatures above the melting point\\u000a using the solutions of the Boltzmann equation. The experimental x-ray structure factor of Waseda and the form factor derived\\u000a using the Heine-Abarenkov model potential are used in these calculations. The ratio of the electrical and thermal conductivities\\u000a is calculated and compared
Calculation of spontaneous emission and gain spectra for quantum cascade lasers
Q. K. Yang; A. Z. Li
In this paper, a quantum cascade laser has been treated as a three-level system, and the calculation of the spontaneous emission and gain spectra has been given. In the calculation, the conduction band nonparabolicity and the injection and exit of electrons have been considered. Results have shown that with increasing injection current, the spontaneous emission peak blue shifts, and the
Quantum Monte Carlo: Direct calculation of corrections to trial wave functions and their energies
Anderson, James B.
ARTICLES Quantum Monte Carlo: Direct calculation of corrections to trial wave functions, Pennsylvania 16802 Received 4 January 2000; accepted 10 March 2000 We report an improved Monte Carlo method Monte Carlo QMC method for the direct calculation of corrections to trial wave functions.1Ł3 We report
Theoretical Calculations on Sediment Transport on Titan, and the Possible Production of Streamlined Forms
NASA Technical Reports Server (NTRS)
Burr, D. M.; Emery, J. P.; Lorenz, R. D.
The Cassini Imaging Science System (ISS) has been returning images of Titan, along with other Saturnian satellites. Images taken through the 938 nm methane window see down to Titan's surface. One of the purposes of the Cassini mission is to investigate possible fluid cycling on Titan. Lemniscate features shown recently and radar evidence of surface flow prompted us to consider theoretically the creation by methane fluid flow of streamlined forms on Titan. This follows work by other groups in theoretical consideration of fluid motion on Titan's surface.
Analytic and numerical calculations of quantum synchrotron spectra from relativistic electron distributions
NASA Technical Reports Server (NTRS)
Brainerd, J. J.; Petrosian, V.
Calculations are performed numerically and analytically of synchrotron spectra for thermal and power-law electron distributions using the single-particle synchrotron power spectrum derived from quantum electrodynamics. It is found that the photon energy at which quantum effects appear is proportional to temperature and independent of field strength for thermal spectra; quantum effects introduce an exponential roll-off away from the classical spectra. For power law spectra, the photon energy at which quantum effects appear is inversely proportional to the magnetic field strength; quantum effects produce a steeper power law than is found classically. The results are compared with spectra derived from the classical power spectrum with an energy cutoff ensuring conservation of energy. It is found that an energy cutoff is generally an inadequate approximation of quantum effects for low photon energies and for thermal spectra, but gives reasonable results for high-energy emission from power-law electron distributions.
University and older school students following scientific courses now use complex calculators with graphical, numerical and symbolic capabilities. In this context, the design of lessons for 11th grade pre-calculus students was a stimulating challenge. In the design of lessons, emphasising the role of mediation of calculators and the devel- opment of schemes of use in an 'instrumental genesis' was productive.
Ligand recognition by chloroperoxidase using molecular interaction fields and quantum chemistry calculations
J. C.-Basurto; J. Aburto; J. T.-Ferrara; E. Torres
We recently reported that chloroperoxidase (CPO) from Caldariomyces fumago showed atypical kinetic behavior for the oxidation of 4,6 dimethyl dibenzothiophene (DMDBT). In this work, we undertake the theoretical study of DMDBT docking into CPO's active site, in order to clarify its binding capacity and affinity using molecular interaction fields and quantum mechanical procedure. The results revealed that CPO has two
Symmetry-projected wave functions in quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Shi, Hao; Jimķnez-Hoyos, Carlos A.; RodrĒguez-Guzmßn, R.; Scuseria, Gustavo E.; Zhang, Shiwei
We consider symmetry-projected Hartree-Fock trial wave functions in constrained-path Monte Carlo (CPMC) calculations. Previous CPMC calculations have mostly employed Hartree-Fock (HF) trial wave functions, restricted or unrestricted. The symmetry-projected HF approach results in a hierarchy of wave functions with increasing quality: the more symmetries that are broken and restored in a self-consistent manner, the higher the quality of the trial wave function. This hierarchy is approximately maintained in CPMC calculations: the accuracy in the energy increases and the statistical variance decreases when further symmetries are broken and restored. Significant improvement is achieved in CPMC with the best symmetry-projected trial wave functions over those from simple HF. We analyze and quantify the behavior using the two-dimensional repulsive Hubbard model as an example. In the sign-problem-free region, where CPMC can be made exact but a constraint is deliberately imposed here, spin-projected wave functions remove the constraint bias. Away from half filling, spatial symmetry restoration in addition to that of the spin leads to highly accurate results from CPMC. Since the computational cost of symmetry-projected HF trial wave functions in CPMC can be made to scale algebraically with system size, this provides a potentially general approach for accurate calculations in many-fermion systems.
Isolating vacuum amplitudes in quantum field calculations at finite temperature
Jean-Paul Blaizot; Urko Reinosa
In calculating Feynman diagrams at finite temperature, it is sometimes convenient to isolate subdiagrams which do not depend explicitly on the temperature. We show that, in the imaginary time formalism, such a separation can be achieved easily by exploiting a simple method, due to Gaudin, to perform the sum over the Matsubara frequencies. In order to manipulate freely contributions which
Structure and properties of electronic and hole centers in CsBr from theoretical calculations.
Halliday, M T E; Hess, W P; Shluger, A L
The electronic structure, geometry, diffusion barriers and optical properties of fundamental defects of CsBr are calculated using hybrid functional DFT and TD-DFT methods. The B3LYP functional with a modified exchange contribution has been used in an embedded cluster scheme to model the structure and spectroscopic properties of the self-trapped triplet exciton, interstitial Br atoms and ions, self-trapped holes and Br vacancies. The calculated migration barriers and positions of maxima of optical absorption bands are in good agreement with experiment, justifying the obtained defect geometries. The off-center triplet exciton luminescence energy is also accurately calculated. PMID:26000613
Theoretical calculation of the energy of formation of LiBH 4
Terry J. Frankcombe; Geert-Jan Kroes; Andreas Zuttel
We report density functional theory calculations on the energy of LiBH4, relative to solid B and LiH and gaseous H2. The calculated energy is ?71.3 (?76.1)kJ\\/mol H2 which can be approximately corrected for zero-point energy to give an enthalpy of ?52 (?57)kJ\\/mol H2 at the PW91 (LDA) level, smaller than but similar to the experimental value of ?68.9kJ\\/mol H2. Calculations
Quantum-mechanical calculations of the intensity distribution in spectra of adenine tautomers: I. Spectra of resonant hyper-Raman scattering
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Shcherbakov, R. S.
The spectra of resonant hyper-Raman scattering of five tautomeric forms of adenine have been theoretically determined for the first time based on quantum-mechanical calculations in the Herzberg-Teller approximation. The occurrence of three structures, Ade-N9,N1H+, Ade-N9H(am), and Ade-N7H(am), in an aqueous solution of adenine has been established.
Complex calculators in the classroom: theoretical and practical reflections on teaching pre-calculus
Jean-Baptiste Lagrange
University and older school students following scientific courses now use complex calculators with graphical, numerical and symbolic capabilities. In this context, the design of lessons for 11th grade pre-calculus students was a stimulating challenge.
A theoretical study of functionalized single-wall carbon nanotubes: ONIOM calculations
Tapas Kar; Brahim Akdim; Xiaofeng Duan; Ruth Pachter
In this study, we employed ONIOM calculations to study functionalized single-wall carbon nanotubes (SWCNTs), for assessing an appropriate level of theory for accurate binding energies calculations, particularly by considering ozone adsorption and arylation. Although ONIOM models reproduced the binding energies and geometries in relatively good agreement with the density functional theory B3LYP\\/6-31G* values in some cases, the `same level different
Gold-coated AFM tips for tip-enhanced Raman spectroscopy: theoretical calculation and experimental demonstration.
Meng, Lingyan; Huang, Tengxiang; Wang, Xiang; Chen, Shu; Yang, Zhilin; Ren, Bin
The optimal gold-coated atomic force microscopy (AFM) tip-substrate system for tip-enhanced Raman spectroscopy (TERS) was designed theoretically and demonstrated experimentally. By optimizing the tip, excitation laser, and the substrate, the TERS enhancement factor can be tuned to as high as 9 orders of magnitude, and the spatial resolution could be down to 5 nm. Preliminary experimental results for AFM tips coated with gold layer of different thicknesses reveal that the maximum enhancement can be achieved when the thickness is about 60-80 nm, which is in good agreement with the theoretical prediction. Our results not only provide a deep understanding of the underlying physical mechanism of AFM tip-based TERS, but also guide the rational construction of a working AFM-TERS system with a high efficiency. PMID:26072752
Theoretical calculations of emission of wolframite and scheelite-type tungstate crystals
Nikolaenko, T.; Hizhnyi, Y.; Nedilko, S. [Faculty of Physics, Kyiv National Taras Shevchenko University, 2, block 1, Acad. Hlushkova ave., 03680, Kyiv (Ukraine)
Tungstate crystals AWO{sub 4} (A = Zn,Cd,Pb) are well-known scintillation materials for various applications in science and technology. In recent years the optical properties of these crystals were intensively studied experimentally and theoretically. However, the origin of luminescence in lead, cadmium and zinc tungstates is still the subject of discussion. According to generally accepted view, the centers of luminescence in AWO{sub 4} crystals are in some or other way related to the tungstate anionic groups. We developed a cluster approach in theoretical investigation of the electronic structure of AWO{sub 4} tungstate crystals based on the configuration interaction (CI) computation in which the lattice vibrations were taken into account.
Spectroscopic analysis of cinnamic acid using quantum chemical calculations
NASA Astrophysics Data System (ADS)
Vinod, K. S.; Periandy, S.; Govindarajan, M.
In this present study, FT-IR, FT-Raman, 13C NMR and 1H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The 13C and 1H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO-LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed.
Theoretical calculations of the total and ionization cross sections for electron impact on some simple biomolecules
NASA Astrophysics Data System (ADS)
Vinodkumar, Minaxi; Joshipura, K. N.; Limbachiya, Chetan; Mason, Nigel
In this paper we report total cross sections (TCS), QT , total elastic cross sections, Qel , and total ionization cross section, Qion for electron impact on water, formaldehyde, formic acid, and the formyl radical from circa 15eVto2KeV . The results are compared where possible, with previous theoretical and experimental results and, in general, are found to be in good agreement. The total and elastic cross sections for HCHO, HCOOH, and CHO radical are reported.
A Theoretical Model of Pyramidal InAs/inP Quantum Dots
NASA Astrophysics Data System (ADS)
Alford, Brian
A quantum dot is an atomic-like system consisting of a semiconductor nanoparticle surrounded by an insulator. When an electron in the valence band of the semiconductor becomes excited, the electron-hole pair that is created (called an exiton) acts much like a hydrogen atom. Investigations have demonstrated the potential application of quantum dots for optical switching and optical memory. A model of a truncated pyramidal InAs quantum dot in an InP matrix will be presented and described. The model uses a single band envelope theory that accurately describes the truncated pyramidal shape of the dot. The matrix representation of the Hamiltonian is calculated in a basis consisting of kinetic energy eigenfunctions that vanish on the surface of a cube containing the dot. The eigenvalues of this matrix are the energy levels. These results will then be compared with photoluminescence measurements of energy levels conducted at the Microelectronics-Photonics Center at the University of Arkansas - Fayetteville
The Calculation of Theoretical Chromospheric Models and the Interpretation of the Solar Spectrum
NASA Technical Reports Server (NTRS)
Avrett, Eugene H.
Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Rurucz on the detailed synthesis of the solar spectrum based on opacity data or over 58 million atomic and molecular lines. our goals are: to determine models of the various features observed on the Sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for non-radiative heating, and for solar activity in general.
The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft
NASA Technical Reports Server (NTRS)
Avrett, Eugene H.
Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Kurucz on the detailed synthesis of the solar spectrum based on opacity data for over 58 million atomic and molecular lines. Our goals are to determine models of the various features observed on the Sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for non-radiative heating, and for solar activity in general.
The calculation of theoretical chromospheric models and the interpretation of the solar spectrum
NASA Technical Reports Server (NTRS)
Avrett, Eugene H.
Since the early 1970s we have been developing the extensive computer programs needed to construct models of the solar atmosphere and to calculate detailed spectra for use in the interpretation of solar observations. This research involves two major related efforts: work by Avrett and Loeser on the Pandora computer program for non-LTE modeling of the solar atmosphere including a wide range of physical processes, and work by Kurucz on the detailed synthesis of the solar spectrum based on opacity data for over 58 million atomic and molecular lines. Our goals are to determine models of the various features observed on the sun (sunspots, different components of quiet and active regions, and flares) by means of physically realistic models, and to calculate detailed spectra at all wavelengths that match observations of those features. These two goals are interrelated: discrepancies between calculated and observed spectra are used to determine improvements in the structure of the models, and in the detailed physical processes used in both the model calculations and the spectrum calculations. The atmospheric models obtained in this way provide not only the depth variation of various atmospheric parameters, but also a description of the internal physical processes that are responsible for nonradiative heating, and for solar activity in general.
Dileptons from vector mesons with dropping masses in a nonequilibrium quantum field theoretical framework
C. Greiner; B. Schenke
The influence of time dependent medium modifications of low mass vector mesons on dilepton production is investigated using nonequilibrium quantum field theory. By working in the two-time representation memory effects are fully taken into account. For different scenarios the resulting dilepton yields are compared to quasi-equilibrium calculations and remarkable differences are found leading to the conclusion that memory effects can not be neglected when calculating dilepton yields from heavy ion collisions. Emphasis is put on a dropping mass scenario since it was recently claimed to be ruled out by the NA60 data. Here the memory effects turn out to be particularly important.
Theoretical calculation of the energy of formation of LiBH 4
NASA Astrophysics Data System (ADS)
Frankcombe, Terry J.; Kroes, Geert-Jan; Z³ttel, Andreas
We report density functional theory calculations on the energy of LiBH 4, relative to solid B and LiH and gaseous H 2. The calculated energy is -71.3 (-76.1) kJ/mol H 2 which can be approximately corrected for zero-point energy to give an enthalpy of -52 (-57) kJ/mol H 2 at the PW91 (LDA) level, smaller than but similar to the experimental value of -68.9 kJ/mol H 2. Calculations on four different LiBH 4 phases indicate that alternative phases are not accessible at low temperatures without applying high pressures. These results indicate that complete decomposition to H 2, B and LiH is not an attractive means of obtaining a reversible hydrogen storage system based on LiBH 4.
The theoretical investigation of all-optical polarization switching based on InGaAs(P) Bragg-spaced quantum wells.
Wang, Tao; Li, Gang; Chen, Zheng
The all-optical polarization switch adopting InGaAsP Bragg-spaced quantum wells (BSQWs) is investigated theoretically because it can be compatible with the optical communication system. The theoretical analysis is based on the transfer matrix approach which provides formalism for studying the optical response of the InGaAsP BSQWs. With this theoretical model we calculate the performance characteristics of the switch, which has a high contrast ratio (~31.1dB), a small insert loss (~13dB), and a small switching energy (~30 M W / cm(2) ). The theory can be used as a basis of experimental research of all-optical spin-dependent polarization switching in BSQWs. PMID:18521140
Machine Learning of Parameters for Accurate Semiempirical Quantum Chemical Calculations
We investigate possible improvements in the accuracy of semiempirical quantum chemistry (SQC) methods through the use of machine learning (ML) models for the parameters. For a given class of compounds, ML techniques require sufficiently large training sets to develop ML models that can be used for adapting SQC parameters to reflect changes in molecular composition and geometry. The ML-SQC approach allows the automatic tuning of SQC parameters for individual molecules, thereby improving the accuracy without deteriorating transferability to molecules with molecular descriptors very different from those in the training set. The performance of this approach is demonstrated for the semiempirical OM2 method using a set of 6095 constitutional isomers C7H10O2, for which accurate ab initio atomization enthalpies are available. The ML-OM2 results show improved average accuracy and a much reduced error range compared with those of standard OM2 results, with mean absolute errors in atomization enthalpies dropping from 6.3 to 1.7 kcal/mol. They are also found to be superior to the results from specific OM2 reparameterizations (rOM2) for the same set of isomers. The ML-SQC approach thus holds promise for fast and reasonably accurate high-throughput screening of materials and molecules.
Quantum-field-theoretical approach to phase-space techniques: Generalizing the positive-P representation
Plimak, L.I. [Fachbereich Physik, Universitaet Kaiserslautern, D-67663 Kaiserslautern (Germany); Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand); Fleischhauer, M. [Fachbereich Physik, Universitaet Kaiserslautern, D-67663 Kaiserslautern (Germany); Olsen, M.K. [Instituto de Fisica da Universidade Federal Fluminense, Boa Viagem Cep.: 24210-340, Niteroi-RJ (Brazil); Collett, M.J. [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand)
We present an introduction to phase-space techniques (PST) based on a quantum-field-theoretical (QFT) approach. In addition to bridging the gap between PST and QFT, our approach results in a number of generalizations of the PST. First, for problems where the usual PST do not result in a genuine Fokker-Planck equation (even after phase-space doubling) and hence fail to produce a stochastic differential equation (SDE), we show how the system in question may be approximated via stochastic difference equations (S{delta}E). Second, we show that introducing sources into the SDE's (or S{delta}E's) generalizes them to a full quantum nonlinear stochastic response problem (thus generalizing Kubo's linear reaction theory to a quantum nonlinear stochastic response theory). Third, we establish general relations linking quantum response properties of the system in question to averages of operator products ordered in a way different from time normal. This extends PST to a much wider assemblage of operator products than are usually considered in phase-space approaches. In all cases, our approach yields a very simple and straightforward way of deriving stochastic equations in phase space.
Theoretical calculations of the total and ionization cross sections for electron impact on some simple biomolecules
Vinodkumar, Minaxi [V. P. and R. P. T. P. Science College, Vallabh Vidyanagar-388120 (India); Joshipura, K. N. [Department of Physics, Sardar Patel University, Vallabh Vidyanagar-388120 (India); Limbachiya, Chetan [P. S. Science College, Kadi--382 715 (India); Mason, Nigel [Department of Physics and Astronomy, Open University, Milton Keynes, MK7 6AA (United Kingdom)
In this paper we report total cross sections (TCS), Q{sub T}, total elastic cross sections, Q{sub el}, and total ionization cross section, Q{sub ion} for electron impact on water, formaldehyde, formic acid, and the formyl radical from circa 15 eV to 2 KeV. The results are compared where possible, with previous theoretical and experimental results and, in general, are found to be in good agreement. The total and elastic cross sections for HCHO, HCOOH, and CHO radical are reported.
Quantum and quasiclassical calculations on the OH+CO --> CO2+H reaction
NASA Astrophysics Data System (ADS)
Clary, David C.; Schatz, George C.
Scattering calculations on the OH+CO?CO2+H reaction are reported using both quantum and quasiclassical methods. The rotating bond approximation is used in the quantum calculations. This method explicitly treats the OH vibration and CO rotation in the reactants and the bending vibration and a local CO stretch in the CO2 product. Analogous quasiclassical trajectory computations are also reported. A potential energy surface obtained as a fit to ab initio data is used. The quantum reaction probabilities are dominated by sharp resonances corresponding to vibrationally excited states of the HOCO complex formed in the reaction. The quantum and quasiclassical lifetimes of these resonances compare quite well with measurements made by Wittig et al. Calculations of differential cross sections, rate coefficients, and CO2 vibrational product distributions are also compared with experimental data. The comparisons of quantum and quasiclassical calculations for models that treat explicitly different numbers of degrees of freedom provide detailed insight into the dynamics of the OH+CO reaction.
Theoretical comparison of advanced methods for calculating nitrous oxide fluxes using non-steady state chambers
Technology Transfer Automated Retrieval System (TEKTRAN)
Several flux-calculation (FC) schemes are available for determining soil-to-atmosphere emissions of nitrous oxide (N2O) and other trace gases using data from non-steady-state flux chambers. Recently developed methods claim to provide more accuracy in estimating the true pre-deployment flux (f0) comp...
Comparison between Theoretical Calculation and Experimental Results of Excitation Functions for Production of Relevant Biomedical Radionuclides
Menapace, E. [ENEA, Division for Advanced Physics Technologies, via Don Fiammelli 2, I-40128 Bologna (Italy); Birattari, C.; Bonardi, M.L.; Groppi, F.; Morzenti, S.; Zona, C. [Universita degli Studi di Milano, via F.lli Cervi 201, I-20090 Segrate, Milan (Italy); INFN-Milano, LASA, Radiochemistry Laboratory, via F.lli Cervi 201, I-20090 Segrate, Milan (Italy)
The radionuclide production for biomedical applications has been brought up in the years, as a special nuclear application, at INFN LASA Laboratory, particularly in co-operation with the JRC-Ispra of EC. Mainly scientific aspects concerning radiation detection and the relevant instruments, the measurements of excitation functions of the involved nuclear reactions, the requested radiochemistry studies and further applications have been investigated. On the side of the nuclear data evaluations, based on nuclear model calculations and critically selected experimental data, the appropriate competence has been developed at ENEA Division for Advanced Physics Technologies. A series of high specific activity accelerator-produced radionuclides in no-carrier-added (NCA) form, for uses in metabolic radiotherapy and for PET radiodiagnostics, are investigated. In this work, last revised measurements and model calculations are reviewed for excitation functions of natZn(d,X)64Cu, 66Ga reactions, referring to irradiation experiments at K=38 variable energy Cyclotron of JRC-Ispra. Concerning the reaction data for producing 186gRe and 211At/211gPo (including significant emission spectra) and 210At, most recent and critically selected experimental results are considered and discussed in comparison with model calculations paying special care to pre-equilibrium effects estimate and to the appropriate overall parameterization. Model calculations are presented for 226Ra(p,2n)225Ac reaction, according to the working program of the ongoing IAEA CRP on the matter.
Theoretical calculations of rotationally inelastic collisions of He with NaK(A?(1)?(+)): Transfer of population, orientation, and alignment.
Malenda, R F; Price, T J; Stevens, J; Uppalapati, S L; Fragale, A; Weiser, P M; Kuczala, A; Talbi, D; Hickman, A P
We have performed extensive calculations to investigate thermal energy, rotationally inelastic collisions of NaK (A(1)?(+)) with He. We determined a potential energy surface using a multi-reference configuration interaction wave function as implemented by the GAMESS electronic structure code, and we have performed coupled channel scattering calculations using the Arthurs and Dalgarno formalism. We also calculate the Grawert coefficients B?(j, j') for each j ? j' transition. These coefficients are used to determine the probability that orientation and alignment are preserved in collisions taking place in a cell environment. The calculations include all rotational levels with j or j' between 0 and 50, and total (translational and rotational) energies in the range 0.0002-0.0025 a.u. (?44-550?cm(-1)). The calculated cross sections for transitions with even values of ?j tend to be larger than those for transitions with odd ?j, in agreement with the recent experiments of Wolfe et al. (J. Chem. Phys. 134, 174301 (2011)). The calculations of the energy dependence of the cross sections and the calculations of the fraction of orientation and alignment preserved in collisions also exhibit distinctly different behaviors for odd and even values of ?j. The calculations also indicate that the average fraction of orientation or alignment preserved in a transition becomes larger as j increases. We interpret this behavior using the semiclassical model of Derouard, which also leads to a simple way of visualizing the distribution of the angles between the initial and final angular momentum vectors j and j'. Finally, we compare the exact quantum results for j ? j' transitions with results based on the simpler, energy sudden approximation. That approximation is shown to be quite accurate. PMID:26071704
Scaled Quantum Mechanical scale factors for vibrational calculations using alternate polarized and augmented basis sets with the B3LYP density functional calculation model
NASA Astrophysics Data System (ADS)
Legler, C. R.; Brown, N. R.; Dunbar, R. A.; Harness, M. D.; Nguyen, K.; Oyewole, O.; Collier, W. B.
The Scaled Quantum Mechanical (SQM) method of scaling calculated force constants to predict theoretically calculated vibrational frequencies is expanded to include a broad array of polarized and augmented basis sets based on the split valence 6-31G and 6-311G basis sets with the B3LYP density functional. Pulay's original choice of a single polarized 6-31G(d) basis coupled with a B3LYP functional remains the most computationally economical choice for scaled frequency calculations. But it can be improved upon with additional polarization functions and added diffuse functions for complex molecular systems. The new scale factors for the B3LYP density functional and the 6-31G, 6-31G(d), 6-31G(d,p), 6-31G+(d,p), 6-31G++(d,p), 6-311G, 6-311G(d), 6-311G(d,p), 6-311G+(d,p), 6-311G++(d,p), 6-311G(2d,p), 6-311G++(2d,p), 6-311G++(df,p) basis sets are shown. The double d polarized models did not perform as well and the source of the decreased accuracy was investigated. An alternate system of generating internal coordinates that uses the out-of plane wagging coordinate whenever it is possible; makes vibrational assignments via potential energy distributions more meaningful. Automated software to produce SQM scaled vibrational calculations from different molecular orbital packages is presented.
The extent of disorder and properties of silicate glasses, melts and layer-silicates: Spectroscopic analysis and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Lee, Sung Keun
Silicate glasses and melts have long been studied not only because of their geologic relevance to natural magmas but also because of their technological applications to the glass industry. The inherent aspect of silicate glasses and melts are extent of disorder among framework units and the distribution of internal structural variables. This dissertation is for a systematic exploration of the extent of disorder in silicate glasses, melts and layer-silicates using NMR spectroscopy and analysis both by theoretical prediction based on statistical thermodynamics and by quantum chemical calculations. The objective of the dissertation includes exploration of the consequences of the degree of disorder of the system on physical properties of interest to geologists and material scientists. The degree of randomness in framework in silicate glasses including borosilicate and aluminosilicates was quantified using the models introducing order parameters such as the degree of Al avoidance and the degree of inter-mixing. The model in conjunction with input from high-resolution NMR and quantum chemical calculations was used to calculate the configurational thermodynamic properties in these glasses. We presented general framework for understanding the extent of short-range order in framework silicates, demonstrating that a more complete description of the macroscopic thermodynamic properties of silicates can be derived from information on the degree of framework disorder and provides another strong link between structures of melts and properties. Bond angle and length distributions, one aspect of topological disorder in this system, were also quantified using these methods. 17O MQ (multiple quantum) MAS NMR at high fields were applied to better understand reactivity of oxygen sites in layer silicates which are one of the most dominant constituents of the Earth's surfaces. Several basal and apical oxygen sites in model clay minerals were resolved, providing improved prospects for atomic scale understanding on the geochemical processes such as weathering.
Theoretical calculation of absorption intensities of C2H and C2D
NASA Astrophysics Data System (ADS)
Tarroni, Riccardo; Carter, Stuart
The theory of dipole-allowed absorption intensities in triatomic molecules is presented for systems with three close-lying electronic states of doublet multiplicity. Its derivation is within the framework of a recently developed variational method [CARTER, S., HANDY, N. C., PUZZARINI, C., TARRONI, R., and PALMIERI, P., 2000, Molec. Phys., 98, 1967]. The method has been applied to the calculation of the infrared absorption spectrum of the C2H radical and its deuterated isotopomer for energies up to 10 000 cm-1 above the ground state, using highly accurate ab initio diabatic potential energy and dipole moment surfaces. The calculated spectra agree very well with those recorded experimentally in a neon matrix [FORNEY, D., JACOX, M. E., and THOMPSON, W. E., 1995, J. molec. Spectrosc., 170, 178] and assignments in the high energy region of the IR spectra are proposed for the first time.
Theoretical calculation of the solar diurnal variation of the cosmic ray intensity
K. Nagashima; V. R. Potnis; M. A. Pomerantz
SummaryĀĀBy formulating an expression for the anisotropy of the primary cosmic ray intensity, the expected solar diurnal variation\\u000a of the intensity of the nucleonic component of the cosmic radiation at sea level is calculated at various geomagnetic latitudes\\u000a and longitudes for the following cases: (a) the anisotropy is produced outside the terrestrial magnetic field (extra-terrestrial origin), and (b) the anisotropy
Methacrolein in the IR Atmospheric Window: Mm-Wave and FTIR Spectroscopies Complemented by Quantum Calculations
NASA Astrophysics Data System (ADS)
Zakharenko, Olena; Aviles Moreno, Juan-Ramon; Imane, Haykal; Motiyenko, R. A.; Huet, T. R.; Pirali, Olivier
Methacrolein, CH_2=C(CH_3)CHO or MAC, is an important atmospheric molecule because it is a major product of the isoprene-OH reaction. Meanwhile the spectroscopic information on MAC is very scarse. On the theoretical side, we have performed quantum calculations at different levels of theory (DFT and ab initio) to model the structure of the two conformers, the large amplitude motion associated with the methyl top, and the anharmonic vibrational structure. On the experimental side, we have at first characterized the millimeter-wave spectrum of MAC in the 150-465 GHz range using the Lille frequency multiplication chain spectrometer. In particular the ground state has been analyzed up to J, K_a = 37, 17 and the first excited states are currently investigated. Secondly, FTIR spectra have been recorded on the AILES beamline of SOLEIL using a long path cell, between 30 and 3500 wn at medium resolution (0.5 wn). A few bands of atmospheric interest have also been recorded at higher resolution (0.001 wn). We will report the details of the vibrational analysis, as well as the molecular parameters derived from the analysis of the high resolution spectrum of the c-type band located around 930 wn. Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. The experiment on the AILES beam-line of the synchrotron SOLEIL was performed under project number 20130192. M. Suzuki and K. Kozima, J. Molec. Spectrosc. 38 (1971) 314 J. R. Durig, J. Qiu, B. Dehoff and T. S. Little, Spectrochimica Acta 42A (1986) 89
Quantum-mechanical calculation of the relative line intensities in resonance Raman spectra of adenine-thymine and adenine-uracil molecular base pairs
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Anashkin, A. A.
A quantum-mechanical method of calculation of the relative line intensities in the resonance Raman spectra of polyatomic molecules in the Herzberg-Teller approximation is applied for the first time to the description of the spectra of adenine-thymine and adenine-uracil molecular base pairs. The intensity distribution in the resonance Raman (RR) spectra of these pairs excited by laser radiation at 266, 240, 218, and 200 nm is calculated. Satisfactory agreement with the available experimental data is obtained. The basic features of the intensity distribution are discussed and are theoretically substantiated.
Phenol-benzene complexation dynamics: Quantum chemistry calculation, molecular dynamics simulations, and two dimensional IR spectroscopy
Kijeong Kwac; Chewook Lee; Yousung Jung; Jaebeom Han; Kyungwon Kwak; Junrong Zheng; M. D. Fayer; Minhaeng Cho
Molecular dynamics (MD) simulations and quantum mechanical electronic structure calculations are used to investigate the nature and dynamics of the phenol-benzene complex in the mixed solvent, benzene?CCl4. Under thermal equilibrium conditions, the complexes are continuously dissociating and forming. The MD simulations are used to calculate the experimental observables related to the phenol hydroxyl stretching mode, i.e., the two dimensional infrared
Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances
Y. Fujiwara; Y. Tanimoto
On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 \\/ 6-311+G(d,p) was found to give
Symmetry-adapted calculations of strain and polarization fields in (111)-oriented zinc-blende quantum dots
NASA Astrophysics Data System (ADS)
Schulz, S.; Caro, M. A.; O'Reilly, E. P.; Marquardt, O.
We present expressions for the elastic and first-order piezoelectric tensor in (111)-oriented III-V zinc-blende semiconductors. Moreover, an equation for the second-order piezoelectric polarization vector in these systems is derived. Together these expressions provide an efficient route to calculate built-in potentials and strain fields in (111)-oriented zinc-blende nanostructures. Our detailed analysis provides insight into the key parameters that modify strain and built-in fields in a (111)-oriented zinc-blende system compared to a conventional (001) structure. We show that the calculated strain field in a (111)-oriented quantum dot displays the correct C3v symmetry of the underlying crystal structure, even though we use a continuum-based approach and the quantum dot geometry is higher in symmetry than C3v, e.g., C?v. This behavior originates from an in-plane angle dependence of certain elastic tensor components in the (111)-zinc-blende system. In addition, we compare the elastic and the first-order piezoelectric tensor of the (111)-zinc-blende systems with the corresponding quantities in a wurtzite structure and point out similarities and differences. This comparison provides, for example, insight into the sign of the shear piezoelectric coefficient e15 in the wurtzite system, which is still under debate in the literature. Our analysis indicates e15<0, in accordance with recent experimental and theoretical results.
a Constructive Quantum Field Theoretic Approach to Chern-Simons Theory
NASA Astrophysics Data System (ADS)
Nill, Florian
Chern-Simons theory is formulated quantum field theoretically in terms of string operators, which are localized on finite non-selfintersecting paths in the zero-time plane R2. It is shown how the Weyl algebra approach to the abelian Chern-Simons theory leads to a bundle theoretic construction of these æChern-Simons string operatorsÆ. To proceed to the non-abelian case topological Chern-Simons theory is considered as a specific model of a more general theory describing the quantum kinematics of coloured framed Plek ton s in R2. This theory allows the construction of string operators as pair-creation operators, mapping n-Plekton states into (n+2)-Plekton states. Link invariants are obtained as vacuum correlation functions of string operators and obey a natural version of reflection positivity. The vacuum sector of such a purely kinematical Plekton theory may be recovered from the link invariants by Osterwalder-Schrader reconstruction. To make the theory work one needs the structures of a ribbon graph category, for which the representations of a quasi-triangular quasi-Hopf algebra may serve as a specific realization.
Proton transfer in acetaldehyde and acetaldehyde-water clusters: Vacuum ultraviolet photoionization experiment and theoretical calculations
NASA Astrophysics Data System (ADS)
Kostko, Oleg; Troy, Tyler P.; Bandyopadhyay, Biswajit; Ahmed, Musahid
Acetaldehyde, a probable human carcinogen and of environmental importance, upon solvation provides a test bed for understanding proton transfer pathways and catalytic mechanisms. In this study, we report on single photon vacuum ultraviolet photoionization of small acetaldehyde and acetaldehyde-water clusters. Appearance energies of protonated clusters are extracted from the experimental photoionization efficiency curves and compared to electronic structure calculations. The comparison of experimental data to computational results provides mechanistic insight into the fragmentation mechanisms of the observed mass spectra. Using deuterated water for isotopic tagging, we observe that proton transfer is mediated via acetaldehyde and not water in protonated acetaldehyde-water clusters.
The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft
NASA Technical Reports Server (NTRS)
Avrett, E. H.
Solar chromospheric models are described. The models included are based on the observed spectrum, and on the assumption of hydrostatic equilibrium. The calculations depend on realistic solutions of the radiative transfer and statistical equilibrium equations for optically thick lines and continua, and on including the effects of large numbers of lines throughout the spectrum. Although spectroheliograms show that the structure of the chromosphere is highly complex, one-dimensional models of particular features are reasonably successful in matching observed spectra. Such models were applied to the interpretation of chromospheric observations.
Correlation of theoretical calculations and experimental measurements of damage around a shaft in salt
Munson, D.E.; Holcomb, D.J. [Sandia National Labs., Albuquerque, NM (United States); DeVries, K.L.; Brodsky, N.S. [RE/SPEC, Inc., Rapid City, SD (United States); Chan, K.S. [Southwest Research Inst., San Antonio, TX (United States)
Cross-hole ultrasonic measurements were made in the immediate wall of the Air Intake Shaft of the Waste Isolation Pilot Plant facility. These measurements show that compressional wave speed markedly decreases at the shaft wall and then increases with radial distance from the shaft to eventually become that of solid or undamaged salt. This behavior is indicative of deformation damage or microfractures in the salt. These in situ data are compared to both laboratory measurements of wave speed as a function of volume dilatancy and to calculations based on the Multimechanism Deformation Coupled Fracture model, with reasonable agreement.
Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTF-quinones
NASA Astrophysics Data System (ADS)
Karakas, A.; Migalska-Zalas, A.; El Kouari, Y.; Gozutok, A.; Karakaya, M.; Touhtouh, S.
To investigate microscopic third-order nonlinear optical (NLO) behaviour of two tetrathiafulvalene (TTF) derivatives, TTF-diquinone triad (1) and TTF-monoquinone dyad (2), we have computed both dispersion-free and also dispersion of dipole polarizabilities (?) and third-order hyperpolarizabilities (?) at 532 nm wavelength using time-dependent Hartree-Fock (TDHF) method. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by means of configuration interaction (CI) method with all doubly occupied molecular orbitals. We have also calculated the dynamic third-order susceptibilities (?(3)) using the TDHF method. Our theoretical results on the maximum OPA wavelengths, third-order susceptibilities and corresponding microscopic NLO responses are in good agreement with the previous experimental observations of the examined TTF-based molecules. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO-LUMO band gaps for 1 and 2 have been evaluated by density functional theory (DFT) quantum mechanical calculations at B3LYP/6-31G(d, p) level.
Phase diagram of the 3D quantum anisotropic XY modelŚA quantum Monte Carlo calculation
NASA Astrophysics Data System (ADS)
GuimarŃes, M.; Costa, B. V.; Pires, A. S. T.; Souza, A.
In this work we apply the stochastic series expansion quantum Monte Carlo method to study the quantum phase transition of the spin 1 three-dimensional XY model with easy-plane anisotropy D. We simulate this model in cubic lattices (LūLūL) with L?(4,24) and periodic boundary condition. Using finite size scaling we obtained the phase diagram for the model, the critical exponent z?=0.501(5) and the quantum critical point Dc=9.7950(3)J. Using a low temperature expansion for the magnetic susceptibility we obtained z?=0.59(1).
Combined spectral experiment and theoretical calculation to study the interaction of 1,4-dihydroxyanthraquinone for metal ions in solution
NASA Astrophysics Data System (ADS)
Yin, Caixia; Zhang, Jingjing; Huo, Fangjun
The interaction between 1,4-dihydroxyanthraquinone (1,4-DHA) and metal ions was studied by UV-Visible and fluorescence spectroscopies in solution. Time-dependent density functional theory calculations confirmed complex structures. The investigation results showed 1,4-DHA can selectively respond some metal ions and can be monitored by UV-Vis, fluorescence spectra and naked-eye. So 1,4-DHA has a potential application in the design of metal ions probe. More, as typical metal ions, Hg2+ and Er3+, their reaction abilities for 1,4-DHA were studied in detailed. Experimental results showed they have better response for 1,4-DHA. And theoretical calculation concluded that Er3+ easily reacts with 1,4-DHA over Hg2+ attributed to the low reaction energy of Er3+-1,4-DHA than Hg2+-1,4-DHA.
New theoretical method for calculating the radiative association cross section of a triatomic molecule: Application to N2-H-
Stoecklin, T; Hochlaf, M
We present a new theoretical method to treat the atom diatom radiative association within a time independent approach. This method is an adaptation of the driven equations method developed for photodissociation. The bound states energies and wave functions of the molecule are calculated exactly and used to propagate the overlap with the initial scattering wave function. In the second part of this paper, this approach is applied to the radiative association of the N2H- anion. The main features of the radiative association cross sections are analysed and the magnitude of the calculated rate coefficient at 10 Kelvin is used to discuss the existence of the N2H- in the interstellar medium which could be used as a tracer of both N2 and H-.
A new theoretical method for calculating the radiative association cross section of a triatomic molecule: application to N2-H-.
Stoecklin, T; Lique, F; Hochlaf, M
We present a new theoretical method to treat the atom-diatom radiative association within a time independent approach. This method is an adaptation of the driven equations method developed for photodissociation. The bound state energies and wave functions of the molecule are calculated exactly and used to propagate the overlap with the initial scattering wave function. In the second part of this paper, this approach is applied to the radiative association of the N2H(-) anion. The main features of the radiative association cross sections are analysed and the magnitude of the calculated rate coefficient at 10 K is used to discuss the existence of the N2H(-) in the interstellar medium which could be used as a tracer of both N2 and H(-). PMID:23868402
The calculation of theoretical chromospheric models and the interpretation of solar spectra from rockets and spacecraft
NASA Technical Reports Server (NTRS)
Avrett, E. H.
Calculated results based on two chromospheric flare models F1 and F2 of Machado, et al., (1980) are presented. Two additional models are included: F1*, which has enhanced temperatures relative to the weak-flare model F1 in the upper photosphere and low chromosphere, and F3 which has enhanced temperatures relative to the strong flare model F2 in the upper chromosphere. Each model is specified by means of a given variation of the temperature as a function of column mass. The corresponding variation of particle density and the geometrical height scale are determined by assuming hydrostatic equilibrium. The coupled equations of statistical equilibrium is solved as is radiative transfer for H, H-, He I-II, C I-IV, Si I-II, Mg I-II, Fe, Al, O I-II, Na, and Ca II. The overall absorption and emission of radiation by lines throughout the spectrum is determined by means of a reduced set of opacities sampled from a compilation of over 10 to the 7th power individual lines. That the white flight flare continuum may arise by extreme chromospheric overheating as well as by an enhancement of the minimum temperature region is also shown. The radiative cooling rate calculations for our brightest flare model suggest that chromospheric overheating provides enhanced radiation that could cause significant heating deep in the flare atmosphere.
``Phantom'' Modes in Ab Initio Tunneling Calculations: Implications for Theoretical Materials Optimization, Tunneling, and Transport
NASA Astrophysics Data System (ADS)
Barabash, Sergey V.; Pramanik, Dipankar
Development of low-leakage dielectrics for semiconductor industry, together with many other areas of academic and industrial research, increasingly rely upon ab initio tunneling and transport calculations. Complex band structure (CBS) is a powerful formalism to establish the nature of tunneling modes, providing both a deeper understanding and a guided optimization of materials, with practical applications ranging from screening candidate dielectrics for lowest ``ultimate leakage'' to identifying charge-neutrality levels and Fermi level pinning. We demonstrate that CBS is prone to a particular type of spurious ``phantom'' solution, previously deemed true but irrelevant because of a very fast decay. We demonstrate that (i) in complex materials, phantom modes may exhibit very slow decay (appearing as leading tunneling terms implying qualitative and huge quantitative errors), (ii) the phantom modes are spurious, (iii) unlike the pseudopotential ``ghost'' states, phantoms are an apparently unavoidable artifact of large numerical basis sets, (iv) a presumed increase in computational accuracy increases the number of phantoms, effectively corrupting the CBS results despite the higher accuracy achieved in resolving the true CBS modes and the real band structure, and (v) the phantom modes cannot be easily separated from the true CBS modes. We discuss implications for direct transport calculations. The strategy for dealing with the phantom states is discussed in the context of optimizing high-quality high- ? dielectric materials for decreased tunneling leakage.
Vibrational spectroscopic studies (FT-IR, FT-Raman, SERS) and quantum chemical calculations on cyclobenzaprinium salicylate.
Mary, Y Shyma; Jojo, P J; Van Alsenoy, Christian; Kaur, Manpreet; Siddegowda, M S; Yathirajan, H S; Nogueira, Helena I S; Cruz, Sandra M A
FT-IR, FT-Raman and surface enhanced Raman scattering spectra of cyclobenzaprinium salicylate were recorded and analyzed. The vibrational wavenumbers were examined theoretically using the Gaussian09 set of quantum chemistry codes, and the normal modes were assigned by potential energy distribution calculations. The downshift of the OH stretching frequency is due to strong hydrogen bonded system present in the title compound as given by XRD results. The presence of CH3, CH2 and CO2 modes in the SERS spectrum indicates the nearness of the methyl group to the metal surface which affects the orientation and metal molecule interaction. The presence of phenyl ring modes in the SERS spectrum indicates a tilted orientation with respect to the metal surface. The geometrical parameters of the title compound are in agreement with XRD results. A computation of the first hyperpolarizability indicates that the compound may be a good candidate as a NLO material. PMID:24200648
Theoretical calculation of femtosecond time-resolved spectra of initial electron transfer in photosynthetic reaction centers
Lin, S.H.; Alden, R.G.; Hayashi, M.; Suzuki, Satoru; Murchison, H.A. (Arizona State Univ., Tempe, AZ (United States))
In this paper, we propose to study the dynamics and spectroscopy of photosynthetic reaction centers (RCs). We shall analyze the experimental femtosecond spectra of Rb. sphaeroides (R-26) which usually consist of contributions from populations and coherences. We shall extract information on vibrational relaxation, electron transfer (ET), and the vibrational modes involved in ET from the analysis of the femtosecond time-resolved spectra with pronounced coherence contributions. Conventional ET theory assumes that vibrational relaxation (VR) is much faster than ET so that the vibrational equilibrium is established before ET takes place. However, the primary ET in RCs occurs in 1-4 ps. This implies that this assumption should be examined. We shall study theoretically the effect of the excitation wavelength; that is, we shall study how the ET in RCs is affected by exciting to different vibronic states of RCs. In the dynamic aspect of primary ET in RCs, these experiments will provide us not only with the mechanism of ET but also with the vibrational relaxation of various modes involved in ET. In this case, it is necessary to know the expressions of single-vibronic level ET rate constants. This will also be presented in this paper. 45 refs., 6 figs., 1 tab.
Quantum calculations on salt bridges with water: Potentials, structure, and properties
Sing Liao; Michael E. Green
Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with
Quantum Monte Carlo calculations of electronic excitation energies: the case of the singlet n
Paris-Sud XI, Universitķ de
) transition in acrolein Julien Toulouse1 , Michel Caffarel2 , Peter Reinhardt1 , Philip E. Hoggan3 , and C. J-of-the-art quantum Monte Carlo calculations of the singlet n (CO) vertical excitation energy in the acrolein in the acrolein molecule without reoptimization of the determinantal part of the wave function. The acrolein
YoungÆs modulus calculations for cellulose I▀ by MM3 and quantum mechanics
Technology Transfer Automated Retrieval System (TEKTRAN)
Quantum mechanics (QM) and molecular mechanics (MM) calculations were performed to elucidate YoungÆs moduli for a series of cellulose I▀ models. Computations using the second generation empirical force field MM3 with a disaccharide cellulose model, 1,4'-O-dimethyl-▀-cellobioside (DMCB), and an analo...
An exact quantum Monte Carlo calculation of the helium-helium intermolecular potential
Anderson, James B.
An exact quantum Monte Carlo calculation of the helium-helium intermolecular potential James B Monte Carlo method used is exact in that it requires no mathematical or physical approximations beyond those of the Schriidinger equation. As in most Monte Carlo methods there is a statistical or sampling
Playing the quantum shuffling game with programmable pocket calculators and microcomputers
G. Sauer
The utilisation of programmable calculators or microcomputers in the classroom for the quantum shuffling game may reinforce the study of statistical physics in unit 9 of the Nuffield advanced physics course since the students are themselves able to work out much more sophisticated applications of the game. Because of the higher speed of computation and the possibilities of graphical representation
Thermochemistry and accurate quantum reaction rate calculations for H2\\/HD\\/D2 + CH3
Gunnar Nyman; Rob van Harrevelt; Uwe Manthe
Accurate quantum-mechanical results for thermodynamic data, cumulative reaction probabilities (for J = 0), thermal rate constants, and kinetic isotope effects for the three isotopic reactions H-2 + CH3 -> CH4 + H, HD + CH3 -> CH4 + D, and D-2 + CH3 -> CH3D + D are presented. The calculations are performed using flux correlation functions and the multiconfigurational
Quantum calculations for the photodetachment cross sections of H- located between two walls
NASA Astrophysics Data System (ADS)
Zhao, H. J.; Ma, Z. J.; Du, M. L.
We re-investigate the photodetachment cross sections of H- in a quantum well consisting of two parallel hard walls using a quantum approach. The formulas for the cross sections are explicitly derived and compared with those derived by using closed-orbit theory (G.C. Yang, et al., Physica B 404 (2009) 1576 [15]). The present quantum results confirm the staircase pattern of the cross sections obtained earlier when the polarization of photons is parallel to the normal direction of the walls. However, we find that when the polarization is perpendicular to the normal direction of the walls, oscillations in the cross sections in the present quantum calculations are still present in contrast to the predictions of closed-orbit theory. The differences in the two results are large enough to be observable.
Theoretical calculation of the dislocation width and Peierls barrier and stress for semiconductor silicon.
Wang, Shaofeng; Zhang, Huili; Wu, Xiaozhi; Liu, Ruiping
The dislocation width and Peierls barrier and stress have been calculated by the improved Peierls-Nabarro (PN) theory for silicon. In order to investigate the discreteness correction of a complex lattice quantitatively, a simple dynamics model has been used in which interaction attributed to a variation of bond length and angle has been considered. The results show that the dislocation core and mobility will be corrected significantly by the discrete effect. Another improvement is considering the contribution of strain energy in evaluating the dislocation energy. When a dislocation moves, both strain and misfit energies change periodically. Their amplitudes are of the same order, but phases are opposite. Because of the opposite phases, the misfit and strain energies cancel each other and the resulting Peierls barrier is much smaller than that given by the misfit energy conventionally. Due to competition between the misfit and strain energies, a metastable state appears separately for glide 90░ and shuffle screw dislocations. In addition, from the total energy calculation it is found that besides the width of dislocation, the core of a free stable dislocation may be different according to where the core center is located. The exact position of the core center can be directly verified by numerical simulation, and provides a new prediction that can be used to verify the validity of PN theory. It is interesting that after considering discrete correction the Peierls stress for glide dislocation coincides with the critical stress at low temperature, and the Peierls stress for shuffle dislocation coincides with the critical stress at high temperature. The physical implication of the results is discussed. PMID:21386349
Accuracy of Theoretical OAMO Calculations for Electron-Impact Ionization of Molecules
NASA Astrophysics Data System (ADS)
Chaluvadi, Hari
The study of electron impact single ionization of atoms and molecules has provided valuable information about fundamental collisions. The most detailed information is obtained from triple differential cross sections (TDCS) in which the energy and momentum of all three final state particles are determined. These cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. There are many theoretical approximations for ionization of molecules. One of the successful methods is the distorted wave (DW) approximation. One of the strengths of the DW approximation is that it can be applied for any energy and any size molecule. One of the approximations that has been made to significantly reduce the required computer time is the OAMO (orientation averaged molecular orbital) approximation. Surprisingly, the M3DW-OAMO approximation yields reasonably good agreement with experiment for ionization of H2 by both low and intermediate energy incident electrons. On the other hand, the M3DW-OAMO results for ionization of CH4 and NH3 did not agree very well with experiment. Consequently, we decided to check the validity of the OAMO approximation by performing a proper average over orientations and we found much better agreement with experimental data. In this talk we will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of small, medium, and large molecules. The study of electron impact single ionization of atoms and molecules has provided valuable information about fundamental collisions. The most detailed information is obtained from triple differential cross sections (TDCS) in which the energy and momentum of all three final state particles are determined. These cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. There are many theoretical approximations for ionization of molecules. One of the successful methods is the distorted wave (DW) approximation. One of the strengths of the DW approximation is that it can be applied for any energy and any size molecule. One of the approximations that has been made to significantly reduce the required computer time is the OAMO (orientation averaged molecular orbital) approximation. Surprisingly, the M3DW-OAMO approximation yields reasonably good agreement with experiment for ionization of H2 by both low and intermediate energy incident electrons. On the other hand, the M3DW-OAMO results for ionization of CH4 and NH3 did not agree very well with experiment. Consequently, we decided to check the validity of the OAMO approximation by performing a proper average over orientations and we found much better agreement with experimental data. In this talk we will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of small, medium, and large molecules. This work is supported by the US National Science Foundation under Grant. No. PHY - 1068237. Computational work was performed with Institutional resources made available through Los Alamos National Laboratory.
Studies on the interaction between 9-fluorenylmethyl chloroformate and Fe3+ and Cu2+ ions: spectroscopic and theoretical calculation approach.
Gu, Zhenyan; Lei, Wu; Shi, Wenyan; Hao, Qingli; Si, Weimeng; Xia, Xifeng; Wang, Fengxiang
The interaction between 9-fluorenylmethyl chloroformate (FMOC-Cl) and Fe3+ and Cu2+ ions was investigated using fluorescence, UV/Vis absorption spectroscopies and theoretical calculation. The optical property of FMOC-Cl was studied in detail in absence and presence of various transition metal ions with particular affinity to Fe3+ and Cu2+ ions. With the fluorescence characteristic band centered at 307 and 315 nm for FMOC-Cl, the introduction of Fe3+ or Cu2+ ions leads to the fluorescence quenching of FMOC-Cl with different shift and intensities of two fluorescent bands. It allows us to differentiate between FMOC-Cl and Fe3+ and Cu2+ ions interaction behavior. The study on fluorescent kinetics confirms that the fluorescence quenching of FMOC-Cl with Fe3+ and Cu2+ ions is based on the formation of non-fluorescent material, that is, static quenching. Further analyses of bond lengths, Mulliken atomic charges and the frontier orbital compositions for FMOC-Cl and its complexes with Fe3+ and Cu2+ ions were carried out. The theoretical calculations prove the fluorescence quenching originates from the formation of coordination bonds between the oxygen atom of the carbonyl group of FMOC-Cl and Fe3+ and Cu2+ ions. The commercially available FMOC-Cl can be used as excellent fluorescent probe toward Fe3+ and Cu2+ ions with high sensitivity. PMID:24887497
Solar absorptivity of metallic layers subject to a short-flash of concentrated solar energy. Theoretical-experimental calculation
NASA Astrophysics Data System (ADS)
de Monte, Filippo; Ferriere, Alain; Beck, James V.
The paper develops a procedure for the theoretical-experimental calculation of the solar absorption coefficient of metallic layers under the action of a short flash of concentrated solar energy. The knowledge of this coefficient is relevant when the solar thermal processing is used to make a quench in a thin superficial layer of metallic slabs. The experimental data of temperature of the sample are obtained using the SURFSOL experimental device at SOLFACE (High Flux Solar Facilities for Europe), France. In particular, the sensors of temperature are located on its back side as the solar radiation impinges the front irradiated one. The theoretical data are obtained solving the nonlinear inverse transient heat conduction problem using the IHCP1D software based on the well-known function specification method (FSM). It gives transient surface heat fluxes as well as temperatures on the irradiated side of the sample using internal temperature histories. Then a transient radial fin model accounts for the heat diffusion in the radial direction and re-calculates the heat fluxes. Once temperatures and heat flows are known, an estimate of the solar absorption coefficient of the metallic layer (during the flash solar heating process) may be obtained as a function of temperature (AISI 316L steel).
Quantum-mechanical calculation of the intensity distribution in the resonance Raman spectrum of benzonitrile
NASA Astrophysics Data System (ADS)
Burova, T. G.; Anashkin, A. A.
A direct quantum-mechanical calculation of the resonance Raman spectrum of a benzonitrile molecule upon excitation with laser radiation at a wavelength of 228.7 nm is performed in the Herzberg-Teller approximation with allowance made for the Duschinsky effect. The results of the calculation are in reasonable agreement with the available experimental data. The intensity distribution in the calculated resonance Raman spectrum of the benzonitrile molecule is compared with the intensity distributions in the spectra of benzene, methyl-substituted benzenes, and halogenated benzenes. It is revealed that the intensity distributions in the resonance Raman spectra of these compounds are characterized by a number of common features.
Ab initio quantum chemical calculation as a tool of evaluating diamagnetic susceptibility of magnetically levitating substances
NASA Astrophysics Data System (ADS)
Fujiwara, Y.; Tanimoto, Y.
On magnetic force evaluation necessary for magnetically levitated diamagnetic substances, isotropic diamagnetic susceptibility estimation by the ab initio quantum chemical calculation using Gaussian03W was verified for more than 300 molecules in a viewpoint of the accuracy in the absolute value and the calculation level affording good cost performance. From comparison, the method of B3PW91 / 6-311+G(d,p) was found to give the adequate absolute value by the relation of (observed) = (1.03 ▒ 0.005) x (calculated) - (1.22 ▒ 0.60) x 10-6 in a unit of cm3 mol-1 and good cost performance.
Efficiency of free-energy calculations of spin lattices by spectral quantum algorithms
Master, Cyrus P.; Yamaguchi, Fumiko [Quantum Entanglement Project, ICORP, JST, Stanford University, Stanford, California 94305-4085 (United States); Yamamoto, Yoshihisa [Quantum Entanglement Project, ICORP, JST, Stanford University, Stanford, California 94305-4085 (United States); NTT Basic Research Laboratories, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)
Ensemble quantum algorithms are well suited to calculate estimates of the energy spectra for spin-lattice systems. Based on the phase estimation algorithm, these algorithms efficiently estimate discrete Fourier coefficients of the density of states. Their efficiency in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size.
Anharmonic Wave Functions of Proteins: Quantum Self-Consistent Field Calculations of BPTI
NASA Astrophysics Data System (ADS)
Roitberg, Adrian; Gerber, R. Benny; Elber, Ron; Ratner, Mark A.
The harmonic approximation for the potential energy of proteins is known to be inadequate for the calculation of many protein properties. To study the effect of anharmonic terms on protein vibrations, the anharmonic wave functions for the ground state and low-lying excited states of the bovine pancreatic trypsin inhibitor (BPTI) were calculated. The results suggest that anharmonic treatments are essential for protein vibrational spectroscopy. The calculation uses the vibrational self-consistent field approximation, which includes anharmonicity and interaction among modes in a mean-field sense. Properties obtained include the quantum coordinate fluctuations, zero-point energies, and the vibrational absorption spectrum.
Large divalent cations and electrostatic potentials adjacent to membranes. A theoretical calculation.
Carnie, S; McLaughlin, S
We have extended the Gouy-Chapman theory of the electrostatic diffuse double layer by considering the finite size of divalent cations in the aqueous phase adjacent to a charged surface. The divalent cations are modeled as either two point charges connected by an infinitely thin, rigid "rod" or two noninteracting point charges connected by an infinitely thin, flexible "string." We use the extended theory to predict the effects of a cation of length 10 A (1 nm) on the zeta and surface potentials of phospholipid bilayer membranes. The predictions of the rod and string models are similar to one another but differ markedly from the predictions of the Gouy-Chapman theory. Specifically, the extended model predicts that a large divalent cation will have a smaller effect on the potential adjacent to a negatively charged bilayer membrane than a point divalent cation, that the magnitude of this discrepancy will decrease as the Debye length increases, and that a large divalent cation will produce a negative zeta potential on a membrane formed from zwitterionic lipids. These predictions agree qualitatively with the experimental results obtained with the large divalent cation hexamethonium. We discuss the biological relevance of our calculations in the context of the interaction of cationic drugs with receptor sites on cell membranes. PMID:6661491
Infrared spectra and theoretical calculations for Fe, Ru, and Os metal hydrides and dihydrogen complexes.
Wang, Xuefeng; Andrews, Lester
Laser-ablated iron, ruthenium, and osmium atoms react with hydrogen in excess argon, neon and pure hydrogen to produce the FeH(2) molecule, and the FeH(2)(H(2))(3), RuH(H(2))(4), RuH(2)(H(2))(4), and (H(2))MH complexes (M = Fe, Ru, Os), as identified through infrared spectra with D(2) and HD substitution. DFT frequency calculations support the assignment of absorptions observed experimentally. The FeH(2) molecule has a quintet ground state with a quasi-linear structure, and is repulsive to the addition of one more H(2) ligand: however, with three more H(2) ligands, stable triplet and singlet state FeH(2)(H(2))(3) supercomplexes can be formed. The quintet FeH(2) molecule and FeH(2)(H(2))(3) supercomplex undergo reversible near-ultraviolet photochemical rearrangement in solid neon and hydrogen. The RuH(2) molecule has a bent triplet ground state and forms the stable singlet RuH(2)(H(2))(4) supercomplex, but only the latter is observed in these experiments. In like fashion RuH has a quartet ground state and the doublet RuH(H(2))(4) complex is trapped in solid hydrogen. All three (H(2))MH complexes with lower energy than MH(3) are trapped, and no absorptions are observed for MH(3) molecules. PMID:19099441
Crystalline Ice as a Cryoprotectant: Theoretical Calculation of Cooling Speed in Capillary Tubes
Yakovlev, Sergey; Downing, Kenneth H.
It is generally assumed that vitrification of both cells and the surrounding medium provides the best preservation of ultrastructure of biological material for study by electron microscopy. At the same time it is known that the cell cytoplasm may provide substantial cryoprotection for internal cell structure even when the medium crystallizes. Thus vitrification of the medium is not essential for good structural preservation. In contrast, a high cooling rate is an essential factor for good cryopreservation because it limits phase separation and movement of cellular components during freezing, thus preserving the native-like state. Here we present calculations of freezing rates that incorporate the effect of medium crystallization, using finite difference methods. We demonstrate that crystallization of the medium in capillary tubes may increase the cooling rate of suspended cells by a factor of 25-300 depending on the distance from the center. We conclude that crystallization of the medium, for example due to low cryoprotectant content, may actually improve cryopreservation of some samples in a near native state. PMID:21534954
Structural determination of vanillin, isovanillin and ethylvanillin by means of gas electron diffraction and theoretical calculations
NASA Astrophysics Data System (ADS)
Egawa, Toru; Kameyama, Akiyo; Takeuchi, Hiroshi
The molecular structures of vanillin (4-hydroxy-3-methoxybenzaldehyde), isovanillin (3-hydroxy-4-methoxybenzaldehyde) and ethylvanillin (3-ethoxy-4-hydroxybenzaldehyde) were determined by means of gas electron diffraction. Among them, vanillin and ethylvanillin have a vanilla odor but isovanillin smells differently. The nozzle temperatures were 125, 173 and 146 ░C, for vanillin, isovanillin and ethylvanillin, respectively. The results of MP2 and B3LYP calculations with the 6-31G** basis set were used as supporting information. The MP2 calculations predicted that vanillin and isovanillin have two stable conformers and ethylvanillin has four stable conformers. The electron diffraction data were found to be consistent with these conformational compositions. The determined structural parameters ( rg and ? ?) of vanillin are as follows: < r(C-C) ring>=1.397(4) ┼; r(C 1-C aldehyde)=1.471(?) ┼; r(C 3-O Me)=1.374(9) ┼; r(C 4-O H)=1.361(?) ┼; r(O-C Me)=1.428(?) ┼; r(C dbnd6 O)=1.214(8) ┼; < r(C-H)>=1.110(11) ┼; r(O-H)=0.991(?) ┼; ?C 6-C 1-C 2=120.6(2)░; ?C 1-C 2-C 3=118.8(?)░; ?C 1-C 6-C 5=120.1(?)░; ?C 2-C 1-C aldehyde=122.7(18)░; ?C 1-C dbnd6 O=119.4(16)░; ?C 4-C 3-O Me=112.2(12)░; ?C 3-C 4-O H=119.1(?)░; ?C 3-O-C=121.7(29)░. Those of isovanillin are as follows: < r(C-C) ring>=1.402(4) ┼; r(C 1-C aldehyde)=1.479(?) ┼; r(C 4-O Me)=1.369(9) ┼; r(C 3-O H)=1.357(?) ┼; r(O-C Me)=1.422(?) ┼; r(C dbnd6 O)=1.221(9) ┼; < r(C-H)>=1.114(14) ┼; r(O-H)=0.995(?) ┼; ?C 6-C 1-C 2=120.2(3)░; ?C 1-C 2-C 3=119.0(?)░; ?C 1-C 6-C 5=119.9(?)░; ?C 2-C 1-C aldehyde=124.6(25)░; ?C 1-C dbnd6 O=121.3(24)░; ?C 3-C 4-O Me=114.4(12)░; ?C 4-C 3-O H=121.2(?)░; ?C 4-O-C=123.8(26)░. Those of ethylvanillin are as follows: < r(C-C) ring>=1.397(6) ┼; r(C 1-C aldehyde)=1.471(?) ┼; r(C 3-O Et)=1.365(13) ┼; r(C 4-O H)=1.352(?) ┼; r(O-C Et)=1.427(?) ┼; r(C-C Et)=1.494(21) ┼; r(C dbnd6 O)=1.206(9) ┼; < r(C-H)>=1.109(10) ┼; r(O-H)=0.990(?) ┼; ?C 6-C 1-C 2=120.2(3)░; ?C 1-C 2-C 3=118.4(?)░; ?C 1-C 6-C 5=119.7(?)░; ?C 2-C 1-C aldehyde=121.7(21)░; ?C 1-C dbnd6 O=128.8(22)░; ?C 4-C 3-O Et=112.8(14)░; ?C 3-C 4-O H=119.6(?)░; ?C 3-O-C=115.1(27)░; ?O-C-C Et=102.7(28)░. Angle brackets denote average values; parenthesized values are the estimated limits of error (3 ?) referring to the last significant digit; left arrows in the parentheses mean that these parameters are bound to the preceding one.
ELECTRON-ION RECOMBINATION OF Fe XII FORMING Fe XI: LABORATORY MEASUREMENTS AND THEORETICAL CALCULATIONS
Novotny, O.; Hahn, M.; Lestinsky, M.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Badnell, N. R. [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Bernhardt, D.; Mueller, A.; Schippers, S. [Institut fuer Atom- und Molekuelphysik, Justus-Liebig-Universitaet Giessen, D-35392 Giessen (Germany); Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A., E-mail: email@example.com [Max Planck Institute for Nuclear Physics, 69117 Heidelberg (Germany)
We have measured electron-ion recombination for Fe XII forming Fe XI using a merged-beam configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged-beam recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s {yields} 3p and 3p {yields} 3d core excitations. At higher energies, we observe contributions from 3 {yields} N' and 2 {yields} N' core excitation DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 10{sup 3}-10{sup 7} K. We show that the previously recommended DR data for Fe XII significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionally ionized plasmas (CPs). This is contrasted with our MCBP PRRC results, which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Last, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modeling codes.
Quantum Monte Carlo calculations of the energy-level alignment at hybrid interfaces: Role of many-body effects
Wu, Zhigang
Quantum Monte Carlo calculations of the energy-level alignment at hybrid interfaces: Role of many-level alignment at hybrid interfaces, using quantum Monte Carlo calculations to include many-body effects cancellation on both sides of the interface.11,12 However, a hybrid structure composed of two distinct
A theoretical model for molecules interacting with intense laser pulses: The Floquet-based quantum-classical Liouville equation
Illia Horenko; Burkhard Schmidt; Christof Sch³tte
The Floquet-based quantum-classical Liouville equation (F-QCLE) is presented as a novel theoretical model for the interaction of molecules with intense laser pulses. This equation efficiently combines the following two approaches: First, a small but spectroscopically relevant part of the molecule is treated quantum-mechanically while the remaining degrees of freedom are modeled by means of classical molecular dynamics. The corresponding nonadiabatic
Systematic study of finite-size effects in quantum Monte Carlo calculations of real metallic systems
Azadi, Sam
We present a systematic and comprehensive study of finite-size effects in diffusion quantum Monte Carlo calculations of metals. Several previously introduced schemes for correcting finite-size errors are compared for accuracy and efficiency and practical improvements are introduced. In particular, we test a simple but efficient method of finite-size correction based on an accurate combination of twist averaging and density functional theory. Our diffusion quantum Monte Carlo results for lithium and aluminum, as examples of metallic systems, demonstrate excellent agreement between all of the approaches considered.
Theoretical calculations of X-ray absorption spectra of a copper mixed ligand complex using computer code FEFF9
NASA Astrophysics Data System (ADS)
Gaur, A.; Shrivastava, B. D.
The terms X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) refer, respectively, to the structure in the X-ray absorption spectrum at low and high energies relative to the absorption edge. Routine analysis of EXAFS experiments generally makes use of simplified models and several many-body parameters, e.g. mean free paths, many-body amplitude factors, and Debye-Waller factors, as incorporated in EXAFS analysis software packages like IFEFFIT which includes Artemis. Similar considerations apply to XANES, where the agreement between theory and experiment is often less satisfactory. The recently available computer code FEFF9 uses the real-space Green's function (RSGF) approach to calculate dielectric response over a broad spectrum including the dominant low-energy region. This code includes improved treatments of many-body effects such as inelastic losses, core-hole effects, vibrational amplitudes, and the extension to full spectrum calculations of optical constants including solid state effects. In the present work, using FEFF9, we have calculated the X-ray absorption spectrum at the K-edge of copper in a complex, viz., aqua (diethylenetriamine) (isonicotinato) copper(II), the crystal structure of which is unknown. The theoretical spectrum has been compared with the experimental spectrum, recorded by us at the XAFS beamline 11.1 at ELETTRA synchrotron source, Italy, in both XANES and EXAFS regions.
Electron-ion recombination of Fe{sup 12+} forming Fe{sup 11+}: Laboratory measurements and theoretical calculations
Hahn, M.; Novotn², O.; Savin, D. W. [Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027 (United States); Badnell, N. R. [Department of Physics, University of Strathclyde, 107 Rottenrow East, Glasgow G4 0NG (United Kingdom); Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A. [Max-Planck-Institut f³r Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Lestinsky, M. [GSI Helmholtzzentrum f³r Schwerionenforschung, Planckstrasse 1, D-64291 Darmstadt (Germany); M³ller, A.; Schippers, S. [Institut f³r Atom- und Molek³lphysik, Justus-Liebig-Universitõt Giessen, Leihgesterner Weg 217, D-35392 Giessen (Germany)
We have measured dielectronic recombination (DR) for Fe{sup 12+} forming Fe{sup 11+} using the heavy ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Using our results, we have calculated a plasma rate coefficient from these data that can be used for modeling astrophysical and laboratory plasmas. For the low temperatures characteristic of photoionized plasmas, the experimentally derived rate coefficient is orders of magnitude larger than the previously recommended atomic data. The existing atomic data were also about 40% smaller than our measurements at temperatures relevant for collisionally ionized plasmas. Recent state-of-the-art theory has difficulty reproducing the detailed energy dependence of the DR spectrum. However, for the Maxwellian plasma rate coefficient, recent theoretical results agree with our measurements to within about 30% for both photoionized and collisionally ionized plasmas.
Actinometric measurements and theoretical calculations of j/O3/, the rate of photolysis of ozone to O/1D/
NASA Technical Reports Server (NTRS)
Dickerson, R. R.; Stedman, D. H.; Chameides, W. L.; Crutzen, P. J.; Fishman, J.
The paper presents an experimental technique which measures j/O3-O(1-D)/, the rate of solar photolysis of ozone to singlet oxygen atoms. It is shown that a flow actinometer carries dilute O3 in N2O into direct sunlight where the O(1D) formed reacts with N2O to form NO which chemiluminescence detects, with a time resolution of about one minute. Measurements indicate a photolysis rate of 1.2 (+ or - .2) x 10 to the -5/s for a cloudless sky, 45 deg zenith angle, 0.345 cm ozone column and zero albedo. Finally, ground level results compare with theoretical calculations based on the UV actinic flux as a function of ozone column and solar zenith angle.
Structural and electronic properties of Snn-1Pb and Pbn-1Sn clusters: a theoretical investigation through first principles calculations
NASA Astrophysics Data System (ADS)
Barman, S.; Rajesh, C.; Das, G. P.; Majumder, C.
Here we report a systematic theoretical study of the structure and electronic properties of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters and compare these results with pure Snn and Pbn to understand the influence of the dopant elements. The calculations were carried out using the density functional theory with generalized gradient approximation for the exchange-correlation potential. Extensive search based on large number of initial configurations has been carried out to locate the stable isomers of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters. The relative stability of Snn-1Pb and Pbn-1Sn (n = 2-13) clusters is analyzed based on the calculated binding energies and second difference in energy. The stability analysis of these clusters suggests that, while the substitution of Sn by Pb lowers the stability of Snn clusters, presence of Sn enhances the stability of the Pbn clusters. The results suggest that while for Snn-1Pb, n=4, 7, 10, 12 clusters are more stable than their respective neighbors, Pbn-1Sn clusters with n = 4, 7 and 9 are found to be more stable. Based on the fragmentation pattern it is seen that for Snn-1Pb and Pbn-1Sn clusters favor monomer evaporation of the Pb atom up to n =11 and n =12, respectively. Unlike this trend, the Sn11Pb undergoes fission type fragment into Sn5Pb and Sn6 clusters. A comparison between our theoretical results and surface induced dissociation experiment shows good agreement, which gives confidence on the prediction of the ground state geometries.
Novel Method Based on Quantum Chemistry for Calculation of Ion Induced Secondary Electron Emission Coefficient of MgO Surfaces
NASA Astrophysics Data System (ADS)
Serizawa, Kazumi; Onuma, Hiroaki; Kikuchi, Hiromi; Kitagaki, Masaki; Yamashita, Itaru; Suzuki, Ai; Sahnoun, Riadh; Koyama, Michihisa; Tsuboi, Hideyuki; Hatakeyama, Nozomu; Endou, Akira; Takaba, Hiromitsu; Del Carpio, Carlos A.; Kubo, Momoji; Kajiyama, Hiroshi; Miyamoto, Akira
High ion induced secondary electron emission (IISEE) coefficient (?) MgO protecting layers are required in order to decrease the firing voltage of plasma display panels (PDPs). Theoretical calculation of ? for MgO surfaces provides an effective way to design better protecting layers. Here, we have developed a novel ? value estimation method based on an ultra accelerated quantum chemical molecular dynamics simulation considering the collision effect of Ne+ into a flat MgO(100) surface. Compared with experimentally obtained results, our estimated ? values are only marginally different. Our study shows that ? is primarily influenced by impact sites and Ne+ acceleration voltage. To interpret the behavior of ? in terms of these two variables, we analyzed the electronic structure of the MgO surface during the collision of Ne+. Our analyses show that the work function depends on impact sites and Ne+ acceleration voltage since Ne+ interacts with the surface. Our newly developed methodology enabled ? estimation from quantum chemical instances alone, considering the effect of Ne+ collision onto the MgO surface.
Quantum preequilibrium multistep direct calculations for nucleon scattering on deformed nuclei: a microscopic approach
Dupuis, Marc; Kawano, Toshihiko [T-16 Nuclear Physics, Los Alamos National Laboratory, New Mexico (United States); Bonneau, Ludovic [Centre d'etude nucleaire de Bordeaux Gradignan (France)
An introduction of the different quantum mechanics models is given for the calculation of pre-equilibrium multistep direct process for nucleon induced reaction. A practical application is presented for {sup 238}U neutron induced reaction at medium energy (10-20 MeV). The double differential cross-sections are calculated with no adjustable parameter and reproduced the data very well. The cross-sections are expressed as a sum of DWBA transition amplitudes computed with a microscopic two-body interaction. The exited states of the target are expressed as particle-hole excitations built from single particle states obtained with the HF+BCS calculation with a Skyrme force. We also perform a sensitivity study our calculations with respect to the ingredients of the model, namely the two-body interaction which generates the transitions and the target states description.
Efficiency of free energy calculations of spin lattices by spectral quantum algorithms
Cyrus P. Master; Fumiko Yamaguchi; Yoshihisa Yamamoto
Quantum algorithms are well-suited to calculate estimates of the energy spectra for spin lattice systems. These algorithms are based on the efficient calculation of the discrete Fourier components of the density of states. The efficiency of these algorithms in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size.
Efficiency of free energy calculations of spin lattices by spectral quantum algorithms
Master, C P; Yamamoto, Y; Master, Cyrus P.; Yamaguchi, Fumiko; Yamamoto, Yoshihisa
Quantum algorithms are well-suited to calculate estimates of the energy spectra for spin lattice systems. These algorithms are based on the efficient calculation of the discrete Fourier components of the density of states. The efficiency of these algorithms in calculating the free energy per spin of general spin lattices to bounded error is examined. We find that the number of Fourier components required to bound the error in the free energy due to the broadening of the density of states scales polynomially with the number of spins in the lattice. However, the precision with which the Fourier components must be calculated is found to be an exponential function of the system size.
Real-time calculations of many-body dynamics in quantum systems
Takashi Nakatsukasa
Real-time computation of time-dependent quantum mechanical problems are presented for nuclear many-body problems. Quantum tunneling in nuclear fusion at low energy is described using a time-dependent wave packet. A real-time method of calculating strength functions using the time-dependent Schroedinger equation is utilized to properly treat the continuum boundary condition. To go beyond the few-body models,we resort to the density-functional theory. The nuclear mean-field models are briefly reviewed to illustrate its foundation and necessity of state dependence in effective interactions. This state dependence is successfully taken into account by the density dependence, leading to the energy density functional. Photoabsorption cross sections in 238U are calculated with the real-time method for the time-dependent density-functional theory.
Ab initio coupled cluster calculations for nuclei using methods of quantum chemistry
NASA Astrophysics Data System (ADS)
W?och, M.; Dean, D. J.; Gour, J. R.; Piecuch, P.; Hjorth-Jensen, M.; Papenbrock, T.; Kowalski, K.
We report preliminary large scale ab initio calculations of ground and excited states of 16O using quantum chemistry inspired coupled cluster methods and realistic two-body interactions. By using the renormalized Hamiltonians obtained with a no-core G-matrix approach, we obtain the virtually converged results at the level of two-body interactions. Due to the polynomial scaling with the system size that characterizes coupled cluster methods, we can probe large model spaces with up to seven major oscillator shells, for which standard non-truncated shell-model calculations are not possible.
Dynamical basis sets for algebraic variational calculations in quantum-mechanical scattering theory
NASA Technical Reports Server (NTRS)
Sun, Yan; Kouri, Donald J.; Truhlar, Donald G.; Schwenke, David W.
New basis sets are proposed for linear algebraic variational calculations of transition amplitudes in quantum-mechanical scattering problems. These basis sets are hybrids of those that yield the Kohn variational principle (KVP) and those that yield the generalized Newton variational principle (GNVP) when substituted in Schlessinger's stationary expression for the T operator. Trial calculations show that efficiencies almost as great as that of the GNVP and much greater than the KVP can be obtained, even for basis sets with the majority of the members independent of energy.
Auxiliary-field quantum Monte Carlo calculations for systems with long-range repulsive interactions
Silvestrelli, P.L.; Baroni, S.; Car, R. (Forum di Fisica Teorica dell'Instituto Nazionale di Fisica della Materia, Scuola Normale Superiore, piazza dei Cavalieri 7, I-56100 Pisa (Italy) Scuola Internazionale Superiore di Studi Avanzati (SISSA), via Beirut 2/4, I-34014 Trieste (Italy) Institut Romand de Recherche Numerique en Physique des Materiaux (IRRMA), PHB Ecublens, CH-1015 Lausanne (Switzerland))
We report on the first successful attempt to apply the auxiliary-field quantum Monte Carlo technique to the calculation of ground-state properties of systems of many electrons interacting via a Coulomb potential. We have been able to substantially reduce the huge statistical fluctuations arising from the repulsive, long-range character of the interactions, which had so far hindered the application of this method to [ital realistic] Hamiltonians for atoms, molecules, and solids. Our technique is demonstrated with calculations of ground-state properties of the simplest molecular and solid-state systems, i.e., the H[sub 2] molecule and the homogeneous electron gas.
LocalSCF method for semiempirical quantum-chemical calculation of ultralarge biomolecules
N. A. Anikin; V. M. Anisimov; V. L. Bugaenko; V. V. Bobrikov; A. M. Andreyev
A linear-scaling semiempirical method, LocalSCF, has been proposed for the quantum-chemical calculations of ultralarge molecular systems by treating the large-scale molecular task as a variational problem. The method resolves the self-consistent field task through the finite atomic expansion of weakly nonorthogonal localized molecular orbitals. The inverse overlap matrix arising from the nonorthogonality of the localized orbitals is approximated by preserving
Electric-field control of magnetism in graphene quantum dots: Ab initio calculations
Luis A. Agapito; Nicholas Kioussis; Efthimios Kaxiras
Employing ab initio calculations we predict that the magnetic states of hydrogenated diamond-shaped zigzag graphene quantum dots (GQDs), each exhibiting unique electronic structure, can be selectively tuned with gate voltage, through Stark or hybridization electric-field modulation of the spatial distribution and energy of the spin-polarized molecular orbitals, leading to transitions between these states. Electrical read-out of the GQD magnetic state
A regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical-molecular-mechanical calculations
P. K. Biswas
We describe a regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical QM-molecular-mechanical MM calculations. To remedy the nonphysical QM\\/MM Coulomb interaction at short distances arising from a point electrostatic potential ESP charge of the MM atom and also to accommodate the effect of polarized MM atom in the coupling Hamiltonian, we propose a partial-wave expansion of the ESP charge
A regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical-molecular-mechanical calculations
P. K. Biswas; V. Gogonea
We describe a regularized and renormalized electrostatic coupling Hamiltonian for hybrid quantum-mechanical (QM)-molecular-mechanical (MM) calculations. To remedy the nonphysical QM\\/MM Coulomb interaction at short distances arising from a point electrostatic potential (ESP) charge of the MM atom and also to accommodate the effect of polarized MM atom in the coupling Hamiltonian, we propose a partial-wave expansion of the ESP charge
Calculation of primordial matter density contrast in the Quantum Big Bang theory of the cosmological constant
Budh Ram
In the present paper we calculate the amount of primordial mat- ter density contrast in the recent Quantum Big Bang theory (Arxiv: 0705.4549(gr-qc)(2007)) of the cosmological constant. We obtain (??\\/?)M = 1.75 ū 10 5, without the introduction of an adjustable free parameter. Harrison-Zel'dovich k-dependence with A = 64\\/9?2 = 0.72 and n = 1 in |?k|2 = Akn arises
Determination of atropisomeric configurations of macrocyclic bisbibenzyls by HPLC-CD/UV and quantum chemical calculations.
Wang, Li-Ning; Xie, Chun-Feng; Zhu, Xiao-Song; Fan, Pei-Hong; Lou, Hong-Xiang
Isoriccardin C (1) and riccardin D (2), isolated from the liverwort Reboulia hemisphaerica, were first characterized to be a mixture of two enantiomeric atropisomers by online chiral high-performance liquid chromatography-circular dichroism (HPLC-CD) analysis. Exemplarily for bisbibenzyls of the diarylether-biphenyl type, the absolute atropisomeric configurations of compunds 1 and 2 were determined by the analysis of their CD data coupled with quantum chemical CD calculations. PMID:21462034
Calculating the infra-red limit of quantum field theory using analyticity of correlation functions
Lars Kjµrgaard; Paul Mansfield
We describe a general method for calculating the infra-red limit of physical quantities in unitary quantum field theories. Using analyticity of Green functions in a complex scale parameter, the infra-red limit is expressed as a contour integral entirely in the ultra-violet region. The infra-red limit is shown to be the limit of the Borel transform of the physical quantity. The
Quantum dynamics calculation of reaction probability for H + Cl 2 ? HCl + Cl
Shenglong Wang; Xinsheng Zhao
We present in this paper a time-dependent quantum wave packet calculation of the initial state selected reaction probability\\u000a for H + Cl2 based on the GHNS potential energy surface with total angular momentumJ = 0. The effects of the translational, vibrational and rotational excitation of Cl2 on the reaction probability have been investigated. In a broad region of the translational
Helium trimer calculations with a public quantum three-body code
Kolganova, E. A. [Joint Institute for Nuclear Research (Russian Federation); Roudnev, V.; Cavagnero, M. [University of Kentucky, Department of Physics and Astronomy (United States)
We present an illustration of using a quantumthree-body code being prepared for public release. The code is based on iterative solving of the three-dimensional Faddeev equations. The code is easy to use and allows users to perform highly-accurate calculations of quantum three-body systems. The previously known results for He{sub 3} ground state are well reproduced by the code.
Intramolecular hydrogen bonds involving organic fluorine in the derivatives of hydrazides: an NMR investigation substantiated by DFT based theoretical calculations.
Mishra, Sandeep Kumar; Suryaprakash, N
The rare examples of intramolecular hydrogen bonds (HB) of the type the N-HF-C, detected in a low polarity solvent in the derivatives of hydrazides, by utilizing one and two-dimensional solution state multinuclear NMR techniques, are reported. The observation of through-space couplings, such as, (1h)JFH, and (1h)JFN, provides direct evidence for the existence of intra-molecular HB. Solvent induced perturbations and the variable temperature NMR experiments unambiguously establish the presence of intramolecular HB. The existence of multiple conformers in some of the investigated molecules is also revealed by two dimensional HOESY and (15)N-(1)H HSQC experiments. The (1)H DOSY experimental results discard any possibility of self or cross dimerization of the molecules. The derived NMR experimental results are further substantiated by Density Function Theory (DFT) based Non Covalent Interaction (NCI), and Quantum Theory of Atom in Molecule (QTAIM) calculations. The NCI calculations served as a very sensitive tool for detection of non-covalent interactions and also confirm the presence of bifurcated HBs. PMID:25993543
Quantum calculations of the carrier mobility: Methodology, Matthiessen's rule, and comparison with semi-classical approaches
Niquet, Yann-Michel, E-mail: email@example.com; Nguyen, Viet-Hung; Duchemin, Ivan [L-Sim, SP2M, UMR-E CEA/UJF-Grenoble 1, INAC, Grenoble (France); Triozon, Franńois [CEA, LETI-MINATEC, Grenoble (France); Nier, Olivier; Rideau, Denis [ST Microelectronics, Crolles (France)
We discuss carrier mobilities in the quantum Non-Equilibrium Green's Functions (NEGF) framework. We introduce a method for the extraction of the mobility that is free from contact resistance contamination and with minimal needs for ensemble averages. We focus on silicon thin films as an illustration, although the method can be applied to various materials such as semiconductor nanowires or carbon nanostructures. We then introduce a new paradigm for the definition of the partial mobility ?{sub M} associated with a given elastic scattering mechanism ōM,ö taking phonons (PH) as a reference (?{sub M}{sup ?1}=?{sub PH+M}{sup ?1}??{sub PH}{sup ?1}). We argue that this definition makes better sense in a quantum transport framework as it is free from long range interference effects that can appear in purely ballistic calculations. As a matter of fact, these mobilities satisfy Matthiessen's rule for three mechanisms [e.g., surface roughness (SR), remote Coulomb scattering (RCS) and phonons] much better than the usual, single mechanism calculations. We also discuss the problems raised by the long range spatial correlations in the RCS disorder. Finally, we compare semi-classical Kubo-Greenwood (KG) and quantum NEGF calculations. We show that KG and NEGF are in reasonable agreement for phonon and RCS, yet not for SR. We discuss the reasons for these discrepancies.
A Theoretical Mechanism of Szilard Engine Function in Nucleic Acids and the Implications for Quantum Coherence in Biological Systems
Matthew Mihelic, F.
Nucleic acids theoretically possess a Szilard engine function that can convert the energy associated with the Shannon entropy of molecules for which they have coded recognition, into the useful work of geometric reconfiguration of the nucleic acid molecule. This function is logically reversible because its mechanism is literally and physically constructed out of the information necessary to reduce the Shannon entropy of such molecules, which means that this information exists on both sides of the theoretical engine, and because information is retained in the geometric degrees of freedom of the nucleic acid molecule, a quantum gate is formed through which multi-state nucleic acid qubits can interact. Entangled biophotons emitted as a consequence of symmetry breaking nucleic acid Szilard engine (NASE) function can be used to coordinate relative positioning of different nucleic acid locations, both within and between cells, thus providing the potential for quantum coherence of an entire biological system. Theoretical implications of understanding biological systems as such 'quantum adaptive systems' include the potential for multi-agent based quantum computing, and a better understanding of systemic pathologies such as cancer, as being related to a loss of systemic quantum coherence.
Quantum-chemical calculations of the structure and vibration spectrum of methyl nitrate
NASA Astrophysics Data System (ADS)
Shaikhullina, R. M.; Khrapkovskii, G. M.; Sarvarov, F. S.
Methyl nitrate vibration spectra theoretical analysis data within the B3LYP density functional theory method in the 6 -31G (d) basis are represented. When optimizing the geometry of the molecule it was found out that methyl nitrate is characterized by one stable conformation: trans ¢ form. Frequency, intensity and forms of normal vibrations are calculated, their comparative analysis with well-known from the literature experimental data is given.
Theoretical and experimental investigation on tandem Theoretical and experimental investigation on tandem modulator configurations for Frequency Coded Quantum Key Distribution systems
J. Mora; A. Ruiz-Alba; W. Amaya; V. Garcia-Munoz; J. Capmany
We have theoretically and experimentally address the possible tandem electro-optical modulator configurations that can be employed to implement Frequency Coded Quantum Key Distribution systems (FC-QKD). A closed and general formulation of the end to end field propagation in a dispersion compensated FC-QKD optical fiber system under the low modulation index regime is presented which accounts for all the possible tandem combinations. The properties and the parameter selection of the modulators to achieve each one are summarized. We also address which protocol (B92, BB84 or either) is feasible to be implemented with each configuration. The results confirm those reported for the configurations previously reported in the literature and, at the same time, show the existence of four novel tandem modulator configurations that can also be employed. We have also provided experimental evidence of the successful operation of the novel configurations that confirm the behavior predicted by the theoretical results.
SU-E-T-191: First Principle Calculation of Quantum Yield in Photodynamic Therapy
Abolfath, R; Guo, F; Chen, Z; Nath, R [Yale New Haven Hospital, New Haven, CT (United States)
Purpose: We present a first-principle method to calculate the spin transfer efficiency in oxygen induced by any photon fields especially in MeV energy range. The optical pumping is mediated through photosensitizers, e.g., porphyrin and/or ensemble of quantum dots. Methods: Under normal conditions, oxygen molecules are in the relatively non-reactive triplet state. In the presence of certain photosensitizer compounds such as porphyrins, electromagnetic radiation of specific wavelengths can excite oxygen to highly reactive singlet state. With selective uptake of photosensitizers by certain malignant cells, photon irradiation of phosensitized tumors can lead to selective killing of cancer cells. This is the basis of photodynamic therapy (PDT). Despite several attempts, PDT has not been clinically successful except in limited superficial cancers. Many parameters such as photon energy, conjugation with quantum dots etc. can be potentially combined with PDT in order to extend the role of PDT in cancer management. The key quantity for this optimization is the spin transfer efficiency in oxygen by any photon field. The first principle calculation model presented here, is an attempt to fill this need. We employ stochastic density matrix description of the quantum jumps and the rate equation methods in quantum optics based on Markov/Poisson processes and calculate time evolution of the population of the optically pumped singlet oxygen. Results: The results demonstrate the feasibility of our model in showing the dependence of the optical yield in generating spin-singlet oxygen on the experimental conditions. The adjustable variables can be tuned to maximize the population of the singlet oxygen hence the efficacy of the photodynamic therapy. Conclusion: The present model can be employed to fit and analyze the experimental data and possibly to assist researchers in optimizing the experimental conditions in photodynamic therapy.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Kahn, L. R.
The application of ab initio quantum mechanical approaches in the study of metal atom clusters requires simplifying techniques that do not compromise the reliability of the calculations. Various aspects of the implementation of the effective core potential (ECP) technique for the removal of the metal atom core electrons from the calculation were examined. The ECP molecular integral formulae were modified to bring out the shell characteristics as a first step towards fulfilling the increasing need to speed up the computation of the ECP integrals. Work on the relationships among the derivatives of the molecular integrals that extends some of the techniques pioneered by Komornicki for the calculation of the gradients of the electronic energy was completed and a formulation of the ECP approach that quite naturally unifies the various state-of-the-art "shape- and Hamiltonian-consistent" techniques was discovered.
Calculating the infra-red limit of quantum field theory using analyticity of correlation functions
NASA Astrophysics Data System (ADS)
Kjµ rgaard, Lars; Mansfield, Paul
We describe a general method for calculating the infra-red limit of physical quantities in unitary quantum field theories. Using analyticity of Green functions in a complex scale parameter, the infra-red limit is expressed as a contour integral entirely in the ultra-violet region. The infra-red limit is shown to be the limit of the Borel transform of the physical quantity. The method is illustrated by calculating the central charge of the perturbed unitary minimal models and the critical exponents of varphi4 theory in three dimensions. We obtain approximate values for the central charge which are very close to the exact values using only a one loop perturbative calculation. For varphi4 theory we obtain estimates which are within the errors of other more elaborate approaches.
Hybrid theory and calculation of e-N2 scattering. [quantum mechanics - nuclei (nuclear physics)
NASA Technical Reports Server (NTRS)
Chandra, N.; Temkin, A.
A theory of electron-molecule scattering was developed which was a synthesis of close coupling and adiabatic-nuclei theories. The theory is shown to be a close coupling theory with respect to vibrational degrees of freedom but is a adiabatic-nuclei theory with respect to rotation. It can be applied to any number of partial waves required, and the remaining ones can be calculated purely in one or the other approximation. A theoretical criterion based on fixed-nuclei calculations and not on experiment can be given as to which partial waves and energy domains require the various approximations. The theory allows all cross sections (i.e., pure rotational, vibrational, simultaneous vibration-rotation, differential and total) to be calculated. Explicit formulae for all the cross sections are presented.
Microscopic model calculations for the magnetization process of layered triangular-lattice quantum antiferromagnets.
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
Magnetization processes of spin-1/2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H?0.7H_{s}, where H_{s} is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba_{3}CoSb_{2}O_{9} [T. Susuki etĀal., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co^{2+}-based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states. PMID:25635561
Microscopic Model Calculations for the Magnetization Process of Layered Triangular-Lattice Quantum Antiferromagnets
NASA Astrophysics Data System (ADS)
Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei
Magnetization processes of spin-1 /2 layered triangular-lattice antiferromagnets (TLAFs) under a magnetic field H are studied by means of a numerical cluster mean-field method with a scaling scheme. We find that small antiferromagnetic couplings between the layers give rise to several types of extra quantum phase transitions among different high-field coplanar phases. Especially, a field-induced first-order transition is found to occur at H ?0.7 Hs, where Hs is the saturation field, as another common quantum effect of ideal TLAFs in addition to the well-established one-third plateau. Our microscopic model calculation with appropriate parameters shows excellent agreement with experiments on Ba3CoSb2O9 [T. Susuki et al., Phys. Rev. Lett. 110, 267201 (2013)]. Given this fact, we suggest that the Co2 + -based compounds may allow for quantum simulations of intriguing properties of this simple frustrated model, such as quantum criticality and supersolid states.
Unusual mechanism for H{sub 3}{sup +} formation from ethane as obtained by femtosecond laser pulse ionization and quantum chemical calculations
Kraus, Peter M.; Schwarzer, Martin C.; Schirmel, Nora; Urbasch, Gunter; Frenking, Gernot; Weitzel, Karl-Michael [Fachbereich Chemie, Physikalische Chemie, Philipps-Universitaet Marburg, Hans-Meerwein-Strasse, D-35032 Marburg (Germany)
The formation of H{sub 3}{sup +} from saturated hydrocarbon molecules represents a prototype of a complex chemical process, involving the breaking and the making of chemical bonds. We present a combined theoretical and experimental investigation providing for the first time an understanding of the mechanism of H{sub 3}{sup +} formation at the molecular level. The experimental approach involves femtosecond laser pulse ionization of ethane leading to H{sub 3}{sup +} ions with kinetic energies on the order of 4 to 6.5 eV. The theoretical approach involves high-level quantum chemical calculation of the complete reaction path. The calculations confirm that the process takes place on the potential energy surface of the ethane dication. A surprising result of the theoretical investigation is, that the transition state of the process can be formally regarded as a H{sub 2} molecule attached to a C{sub 2}H{sub 4}{sup 2+} entity but IRC calculations show that it belongs to the reaction channel yielding C{sub 2}H{sub 3}{sup +}+ H{sub 3}{sup +}. Experimentally measured kinetic energies of the correlated H{sub 3}{sup +} and C{sub 2}H{sub 3}{sup +} ions confirm the reaction path suggested by theory.
tRNA structure from a graph and quantum theoretical perspective.
Galindo, Johan F; Berm·dez, Clara I; Daza, Edgar E
One of the objectives of theoretical biochemistry is to find a suitable representation of molecules allowing us to encode what we know about their structures, interactions and reactivity. Particularly, tRNA structure is involved in some processes like aminoacylation and genetic code translation, and for this reason these molecules represent a biochemical object of the utmost importance requiring characterization. We propose here two fundamental aspects for characterizing and modeling them. The first takes into consideration the connectivity patterns, i.e. the set of linkages between atoms or molecular fragments (a key tool for this purpose is the use of graph theory), and the second one requires the knowledge of some properties related to the interactions taking place within the molecule, at least in an approximate way, and perhaps of its reactivity in certain means. We used quantum mechanics to achieve this goal; specifically, we have used partial charges as a manifestation of the reply to structural changes. These charges were appropriately modified to be used as weighted factors for elements constituting the molecular graph. This new graph-tRNA context allow us to detect some structure-function relationships. PMID:16337238
Effect of terrestrial radiation on brightness temperature at lunar nearside: Based on theoretical calculation and data analysis
NASA Astrophysics Data System (ADS)
Wei, Guangfei; Li, Xiongyao; Wang, Shijie
Terrestrial radiation is another possible source of heat in lunar thermal environment at its nearside besides the solar illumination. On the basis of Clouds and the Earth's Radiant Energy System (CERES) data products, the effect of terrestrial radiation on the brightness temperature (TBe) of the lunar nearside has been theoretically calculated. It shows that the mafic lunar mare with high TBe is more sensitive to terrestrial radiation than the feldspathic highland with low TBe value. According to the synchronous rotation of the Moon, we extract TBe on lunar nearside using the microwave radiometer data from the first Chinese lunar probe Chang'E-1 (CE-1). Consistently, the average TBe at Mare Serenitatis is about 1.2 K while the highland around the Geber crater (19.4░S, 13.9░E) is relatively small at ?0.4 K. Our results indicate that there is no significant effect of terrestrial radiation on TBe at the lunar nearside. However, to extract TBe accurately, effects of heat flow, rock abundance and subsurface rock fragments which are more significant should be considered in the future work.
The infrared spectra and theoretical calculations of frequencies of fac-tricarbonyl octahedral complexes of manganese(I)
NASA Astrophysics Data System (ADS)
Ault, Bruce S.; Becker, Thomas M.; Li, Guang Qing; Orchin, Milton
The carbonyl stretching frequencies in the infrared spectra of 38 fac-tricarbonyl octahedral complexes of manganese(I) prepared in this laboratory were determined. These complexes may be grouped into three types: (a) neutral complexes of the structure (CO) 3Mn(P-P)Z where P-P represents depe, dppe, or dppp, and Z represents various anionic functional groups bonded to the manganese; (b) ionic complexes of the structure [(CO) 3Mn(P-P)Z] +BF 4- where Z represents various neutral molecules possessing one phosphorous, nitrogen, or oxygen atom coordinated to the manganese; (c) complexes of the structure (CO) 3Mn(pn)Z where the chelating pn represents 1,1-diphenylphosphino-2,2-dimethylaminoethane, Ph 2PCH 2CH 2NMe 2. All of these complexes show three carbonyl stretching modes (2A'+A''). The effects on the frequencies of these modes induced by both the various Z groups and the various ligands are discussed. Theoretical calculations (B3LYP/6-31G) with optimization of the full molecule make it possible to distinguish between the three stretching modes and to make unambiguous assignments of appropriate symmetry species to each.
Decades of Theoretical Work on Protonated Hydrates
NASA Astrophysics Data System (ADS)
Kochanski, E.; Kelterbaum, R.; Klein, S.; Rohmer, M. M.; Rahmouni, A.
Theoretical studies on protonated hydrates (PH) are illustrative of the progress realized in theoretical chemistry over several decades. The evolution of such studies is presented. The main methods used (quantum chemistry, Monte Carlo or Molecular Dynamics calculations...) and the problems encountered are briefly recalled. Some of the results obtained are commented.
A combined quantum-classical dynamics method for calculating thermal rate constants of chemical reactions in solution
Truong, Thanh N.
-flux correlation function for calculating the thermal rate constants of chemical reactions in solution in this study would provide a complete tool for studying the quantum dynamics of chemical reactions the thermal chemical reaction rate constants. Furthermore, we also employ an efficient and accurate quantum
Exploiting the Difference in Probability Calculation between Quantum and Probabilistic Computations
Masami Amano; Kazuo Iwama; Rudy Raymond
The main purpose of this paper is to show that we can exploit the difference ($l_1$-norm and $l_2$-norm) in the probability calculation between quantum and probabilistic computations to claim the difference in their space efficiencies. It is shown that there is a finite language $L$ which contains sentences of length up to $O(n^{c+1})$ such that: ($i$) There is a one-way quantum finite automaton (qfa) of $O(n^{c+4})$ states which recognizes $L$. ($ii$) However, if we try to simulate this qfa by a probabilistic finite automaton (pfa) \\textit{using the same algorithm}, then it needs $\\Omega(n^{2c+4})$ states. It should be noted that we do not prove real lower bounds for pfa's but show that if pfa's and qfa's use exactly the same algorithm, then qfa's need much less states.
Effects of Strain and Quantum Confinement in Optically Pumped Nuclear Magnetic Resonance in GaAs: Interpretation Guided by Spin-Dependent Band Structure Calculations
NASA Astrophysics Data System (ADS)
Bowers, Clifford; Wood, Ryan; Dipta, Saha; Tokarski, John; McCarthy, Lauren; Sanders, Gary; Stanton, Christopher; McGill, Stephen; Reyes, Arneil; Kuhns, Phil; Reno, John
A combined experimental-theoretical study of optically pumped NMR (OPNMR) has been performed in a GaAs/Al0.1Ga0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from the differential absorption to spin-up and spin-down states of the electron conduction band using a modified Pidgeon Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.
New Regularization-Renormalization Method in Quantum Electrodynamics and Qualitative Calculation on Lamb Shift
Guang-jiong Ni; Haibin Wang
A simple but effective method for regularization-renormalization (R-R) is proposed for handling the Feynman diagram integral (FDI) at one loop level in quantum electrodynamics (QED). The divergence is substituted by some constants to be fixed via experiments. So no counter term, no bare parameter and no arbitrary running mass scale is involved. Then the Lamb Shift in Hydrogen atom can be calculated qualitatively and simply as $\\Delta E(2S_{1/2})- \\Delta E(2P_{1/2})=996.7 MHz$ versus the experimental value $1057.85 MHz$.
Quantum-mechanical calculation of the intensity distribution in resonance Raman spectra of guanine
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Kucherova, V. V.
A quantum-mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of guanine is carried out for exciting laser radiation at 266, 240, 218, and 200 nm, which corresponds to resonance with the first four ?-?* transitions. A comparative analysis of the intensity distribution in these spectra is performed. The role played by the Herzberg-Teller effect in description of the intensities of lines in these RR spectra is considered. The general and specific features of the intensity distribution in the RR spectra of adenine, purine, and guanine are discussed.
Playing the quantum shuffling game with programmable pocket calculators and microcomputers
NASA Astrophysics Data System (ADS)
Sauer, G.
The utilisation of programmable calculators or microcomputers in the classroom for the quantum shuffling game may reinforce the study of statistical physics in unit 9 of the Nuffield advanced physics course since the students are themselves able to work out much more sophisticated applications of the game. Because of the higher speed of computation and the possibilities of graphical representation on the computer screen preference is given to the application of microcomputer games. Copies of the programs described may be obtained from Professor P J Black, Chelsea College Centre for Science Education, Bridges Place, London SW6 4HR or directly from the author at Tulpenweg 3, 6301 Linden, W Germany.
Parallelizing the QUDA Library for Multi-GPU Calculations in Lattice Quantum Chromodynamics
Ronald Babich, Michael Clark, Balint Joo
Graphics Processing Units (GPUs) are having a transformational effect on numerical lattice quantum chromodynamics (LQCD) calculations of importance in nuclear and particle physics. The QUDA library provides a package of mixed precision sparse matrix linear solvers for LQCD applications, supporting single GPUs based on NVIDIA's Compute Unified Device Architecture (CUDA). This library, interfaced to the QDP++/Chroma framework for LQCD calculations, is currently in production use on the "9g" cluster at the Jefferson Laboratory, enabling unprecedented price/performance for a range of problems in LQCD. Nevertheless, memory constraints on current GPU devices limit the problem sizes that can be tackled. In this contribution we describe the parallelization of the QUDA library onto multiple GPUs using MPI, including strategies for the overlapping of communication and computation. We report on both weak and strong scaling for up to 32 GPUs interconnected by InfiniBand, on which we sustain in excess of 4 Tflops.
Quantum-mechanical calculation of the intensity distribution in resonance Raman spectra of cytosine
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Kucherova, V. V.
A quantum-mechanical calculation of the relative intensities of lines in resonance Raman (RR) spectra of cytosine excited by laser radiation at 266, 218, and 200 nm was performed in different approximations of the vibronic theory. Both the Herzberg-Teller effect and the contribution from electronic states located close to the resonance state are shown to play a significant role in determining the relative intensities of lines. A satisfactory agreement between the calculated results and experimental data is obtained. The specific features of the intensity distribution in the RR spectra of cytosine are compared with those in the spectra of the previously studied thymine and uracil, which have a similar structure and also belong to the simplest nucleic acid bases.
Phenylazoindole dyes - Part I: The syntheses, characterizations, crystal structures, quantum chemical calculations and antimicrobial properties
NASA Astrophysics Data System (ADS)
Sefero?lu, Zeynel; Yalń?n, Ergin; Bab³r, Banu; Sefero?lu, Nurg³l; H÷kelek, Tuncer; Y?lmaz, Ebru; ?ahin, Ertan
In this study, the synthesis of four new phenylazo indole dyes (dye 1-4) were carried out by diazotization of 4-aminoacetophenone and coupling with various 2- and 1,2-disubstituted indole derivatives. The dyes were characterized by UV-vis, FT-IR, 1H NMR, HRMS and X-ray single crystal diffraction methods. Azo-hydrazone tautomeric bahavior of the dyes in different solvents (DMSO, methanol, acetic acid and chloroform) was investigated by using 1H NMR and UV-vis results. The experimental results were compared with the corresponding calculated values. The results of experimental data and theoretical calculations showed that the azo tautomer is more stable than hydrazone tautomer. In addition to this, the antimicrobial activity of the dyes was also evaluated.
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
I. Tews; S. Gandolfi; A. Gezerlis; A. Schwenk
Chiral effective field theory (EFT) enables a systematic description of low-energy hadronic interactions with controlled theoretical uncertainties. For strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of the most accurate solutions, but they require as input local potentials. We have recently constructed local chiral nucleon-nucleon (NN) interactions up to next-to-next-to-leading order (N$^2$LO). Chiral EFT naturally predicts consistent many-body forces. In this paper, we consider the leading chiral three-nucleon (3N) interactions in local form. These are included in auxiliary field diffusion Monte Carlo (AFDMC) simulations. We present results for the equation of state of neutron matter and for the energies and radii of neutron drops. In particular, we study the regulator dependence at the Hartree-Fock level and in AFDMC and find that present local regulators lead to less repulsion from 3N forces compared to the usual nonlocal regulators.
Rich Information on Quantum States and Ways to Calculate It in The Absorption Spectra of Au144 Gold Cluster Compound
NASA Astrophysics Data System (ADS)
Lopez-Lozano, Xochitl; Whetten, Robert L.; Weissker, Hans-Christian
In recent decades, the prevalent view has been that noble-metal clusters of intermediate size necessarily have smooth optical absorption spectra of low information content in the near-IR, VIS and near-UV regions. At most, one expects a broad, smooth localized surface plasmon resonance feature. Recently, we demonstrate that, in contradistinction to the commonly held view, the optical absorption of the most widely applied gold cluster, the thiolate-protected Au144 cluster, exhibits a rich spectrum of bands that are individually visible over the entire near-IR, VIS and near-UV regions (1.0-4.0 eV), demonstrating high information content related to the quantum size effects which distinguish the nanoparticles from the bulk materials. In the calculation, the result is sensitive to the details of the structure. In the present work, we systematically compare the different structures actually used to date. We studied aspects like symmetry, geometry and type of ligands. In particular, we discuss the effect of their differences on the optical absorption spectra as well as how the theoretical methodology influences the final results.
Structures of the chromophore binding sites in BLUF domains as studied by molecular dynamics and quantum chemical calculations.
Obanayama, Kazuya; Kobayashi, Hiroaki; Fukushima, Kentaro; Sakurai, Minoru
BLUF (blue-light sensing using FAD) domains constitute a new family of flavin-based blue light photoreceptors. The photocycle of BLUF is unique in the sense that a few hydrogen bond rearrangements are accompanied by only slight structural changes in the bound chromophore. The hydrogen bond rearrangements upon illumination have been inferred from spectral changes in the chromophore: approximately 10 nm redshift of the absorption maximum and approximately 16 cm(-1) downshift of the C4=O stretching frequency. However, the exact features of the hydrogen bond network around the active site are still the subject of some controversy. In particular, the orientation of a conserved Gln (Gln63 in AppA) is presently one of the most questioned topics in the field. Here we perform molecular dynamics simulations for the wild-type AppA, AppA1-124C20S, BlrB and T110078 and furthermore quantum chemical calculations to investigate their spectroscopic properties in the dark and signaling states. On the basis of these results, we reveal the dynamic aspect of hydrogen bonding networks at the active site and propose theoretically reasonable models for the dark and signaling states of the BLUF domains. PMID:18435699
Digital radiology using active matrix readout of amorphous selenium: theoretical analysis of detective quantum efficiency.
Zhao, W; Rowlands, J A
A flat-panel x-ray imaging detector using a layer of amorphous selenium (a-Se) for direct conversion of x rays (to charge) and an active matrix for self-scanned readout is being investigated for digital radiology. A theoretical analysis of the spatial frequency dependent detective quantum efficiency (DQE(f)) of the self-scanned a-Se detector is performed based on a model of signal and noise propagation in a cascaded imaging system. Because of the high intrinsic resolution of a-Se and the pixelated active matrix readout method, such detectors are inherently undersampled and aliasing is present. The presampling modulation transfer function (MTF) and aliased noise power spectrum (NPS) of the detector were used in the analysis of DQE(f). It is proven that the aliased NPS for the self-scanned a-Se detectors is white. Since the shape of DQE(f) is determined by the ratio of MTF squared and the NPS, the shape of DQE(f) follows the square of the presampling MTF of the detector as a result of the white NPS. The analysis also shows that DQE(0) is proportional to the pixel fill factor, i.e., the fraction of each pixel area used for image charge collection. The DQE analysis is applied to detector parameters for three x-ray imaging applications: mammography, chest radiography, and fluoroscopy. The effects of pixel fill factor, imaging geometry (i.e., incident angle of x rays), and various sources of electronic noise on the detector DQE(f) are discussed. Strategies for maximizing detector DQE for each x-ray imaging application are proposed. PMID:9434965
Quantum Matching Theory (with new complexity-theoretic, combinatorial and topical insights on the nature of the quantum entanglement)
Gurvits, L. (Leonid)
Classical matching theory can be defined in terms of matrices with nonnegative entries. The notion of Positive operator, central in Quantum Theory, is a natural generalization of matrices with non-negative entries. Based on this point of view, we introduce a definition of perfect Quantum (operator) matching. We show that the new notion inherits many 'classical' properties, but not all of them. This new notion goes somewhere beyound matroids. For separable bipartite quantum states this new notion coinsides with the full rank property of the intersection of two corresponding geometric matroids. In the classical situation, permanents are naturally associated with perfects matchings. We introduce an analog of permanents for positive operators, called Quantum Permanent and show how this generalization of the permanent is related to the Quantum Entanglement. Besides many other things, Quantum Permanents provide new rational inequalities necessary for the separability of bipartite quantum states. Using Quantum Permanents, we give deterministic poly-time algorithm to solve Hidden Matroids Intersection Problem and indicate some 'classical' complexity difficulties associated with the Quantum Entanglement. Finally, we prove that the weak membership problem for the convex set of separable bipartite density matrices is NP-HARD.
ac Josephson Effect in Superfluid Helium in Terms of Action-Angle Variables in Quantum Statistics - A Model Calculation
A. C. Biswas; C. S. Warke
Applying the formalism of action-angle variables in quantum statistics to an exactly solvable model Hamiltonian, explicit expressions have been calculated relating the superfluid tunneling current and the corresponding phase coupling between two helium baths connected by an orifice. The relevance of the calculation to a recent experiment has been pointed out.
Calculation of gain and luminescence spectra of quantum-cascade laser structures taking into account asymmetric emission line broadening
Ushakov, D V; Manak, I S [Belarusian State University, Minsk (Belarus); Kononenko, V K [B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk (Belarus)
The energy levels, wave functions, and matrix elements of optical dipole transitions are calculated numerically for superlattice quantum-cascade structures. The effect of spectral broadening on the shape of emission spectra is estimated and semiphenomenological asymmetric profiles of emission line broadening are proposed. It is shown that the electroluminescence spectra well agree with the calculated spontaneous recombination spectra. (lasers)
The researchers are using kinetics and quantum mechanical calculations to elucidate the catalytic reaction mechanism of hydrocarbon epoxidation.
Ottino, Julio M.
Theory (DFT) and a quantum/classical ONIOM model. For the DFT calculations and for the high-level part of ONIOM, PW91 exchange-correlation functional is used, and the LANL2DZ basis set is employed. For the low-level part of the ONIOM calculations of epoxidation, the UFF force field is utilized. Results: The Broadbelt
Quantum Mechanical Calculations to Interpret Vibrational and NMR Spectra of Organic Compounds Adsorbed onto Mineral Surfaces
NASA Astrophysics Data System (ADS)
Kubicki, J. D.
Vibrational (e.g., ATR FTIR and Raman) and nuclear magnetic resonance (NMR) spectroscopies provide excellent information on the bonding and atomic environment of adsorbed organic compounds. However, interpretation of observed spectra collected for organic compounds adsorbed onto mineral surfaces can be complicated by the lack of comparable analogs of known structure and uncertainties about the mineral surface structure. Quantum mechanical calculations provide a method for testing interpretations of observed spectra because models can be built to mimic predicted structures, and the results are independent of experimental parameters (i.e., no fitting to data is necessary). In this talk, methodologies for modeling vibrational frequencies and NMR chemical shifts of adsorbed organic compounds are discussed. Examples included salicylic acid (as an analog for important binding functional groups in humic acids) adsorbed onto aluminum oxides, organic phosphoryl compounds that represent herbicides and bacterial extracellular polymeric substances (EPS), and ofloxacin (a common agricultural antibiotic). The combination of the ability of quantum mechanical calculations to predict structures, spectroscopic parameters and energetics of adsorption with experimental data on these same properties allows for more definitive construction of surface complex models.
An improved fragment-based quantum mechanical method for calculation of electrostatic solvation energy of proteins
Jia, Xiangyu; Wang, Xianwei; Liu, Jinfeng; Mei, Ye, E-mail: email@example.com, E-mail: firstname.lastname@example.com; He, Xiao, E-mail: firstname.lastname@example.com, E-mail: firstname.lastname@example.com [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China)] [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China); Zhang, John Z. H. [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China) [State Key Laboratory of Precision Spectroscopy, Department of Physics and Institute of Theoretical and Computational Science, East China Normal University, Shanghai 200062 (China); Joint Research Center for Computational Chemistry at NYU Shanghai, Shanghai 200062 (China)
An efficient approach that combines the electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method with conductor-like polarizable continuum model (CPCM), termed EE-GMFCC-CPCM, is developed for ab initio calculation of the electrostatic solvation energy of proteins. Compared with the previous MFCC-CPCM study [Y. Mei, C. G. Ji, and J. Z. H. Zhang, J. Chem. Phys. 125, 094906 (2006)], quantum mechanical (QM) calculation is applied to deal with short-range non-neighboring interactions replacing the classical treatment. Numerical studies are carried out for proteins up to 3837 atoms at the HF/6-31G* level. As compared to standard full system CPCM calculations, EE-GMFCC-CPCM shows clear improvement over the MFCC-CPCM method for both the total electrostatic solvation energy and its components (the polarized solute-solvent reaction field energy and wavefunction distortion energy of the solute). For large proteins with 1000¢4000 atoms, where the standard full system ab initio CPCM calculations are not affordable, the EE-GMFCC-CPCM gives larger relative wavefunction distortion energies and weaker relative electrostatic solvation energies for proteins, as compared to the corresponding energies calculated by the Divide-and-Conquer Poisson-Boltzmann (D and C-PB) method. Notwithstanding, a high correlation between EE-GMFCC-CPCM and D and C-PB is observed. This study demonstrates that the linear-scaling EE-GMFCC-CPCM approach is an accurate and also efficient method for the calculation of electrostatic solvation energy of proteins.
Spectroscopic analysis of 3-Bromodiphenylamine with experimental techniques and quantum chemical calculations.
Sudharsan, A; Seshadri, S; Gnanasambandan, T; Saravanan, R R
In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 3500-100cm(-1) and 4000-400cm(-1), respectively, for 3-Bromodiphenylamine (3BDPA). Theoretical calculations were performed by using Density Functional Theory (DFT) method with 6-31G(d,p) and 6-311++G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The calculated wavenumbers were applied to simulate spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (?0) and related properties (?, ? and ??) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the ?(*) and ?(*) anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. Molecular electrostatic potential (MEP) and HOMO-LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature. PMID:24835947
Thermochemistry and Charge Delocalization in Cyclization Reactions Using Accurate Quantum Monte Carlo Calculations
NASA Astrophysics Data System (ADS)
Saritas, Kayahan; Grossman, Jeffrey C.
Molecules that undergo pericyclic isomerization reactions find interesting optical and energy storage applications, because of their usually high quantum yields, large spectral shifts and small structural changes upon light absorption. These reactions induce a drastic change in the conjugated structure such that substituents that become a part of the conjugated system upon isomerization can play an important role in determining properties such as enthalpy of isomerization and HOMO-LUMO gap. Therefore, theoretical investigations dealing with such systems should be capable of accurately capturing the interplay between electron correlation and exchange effects. In this work, we examine the dihydroazulene isomerization as an example conjugated system. We employ the highly accurate quantum Monte Carlo (QMC) method to predict thermochemical properties and to benchmark results from density functional theory (DFT) methods. Although DFT provides sufficient accuracy for similar systems, in this particular system, DFT predictions of ground state and reaction paths are inconsistent and non-systematic errors arise. We present a comparison between QMC and DFT results for enthalpy of isomerization, HOMO-LUMO gap and charge densities with a range of DFT functionals.
Vibrational Spectra, Theoretical Calculations, and Structures of Cyclic Silanes, 2,4,7-Trioxa(3.3.0)Octane and BotryococcenesĀ
Chun, Hye Jin
of the twist minima. The vibrational assignments of 2,4,7-trioxa(3.3.0)octane have been made based on its infrared and Raman spectra and theoretical DFT calculations. The two ring-puckering motions (in-phase and out-of-phase) were observed in the Raman spectrum...
Research on the chelation between luteolin and Cr(III) ion through infrared spectroscopy, UV-vis spectrum and theoretical calculations
NASA Astrophysics Data System (ADS)
Gao, Li-Guo; Wang, Hua; Song, Xiao-Li; Cao, Wei
The chelation between luteolin and Cr(III) ion is studied using the theoretical methods. Many different potential complexes, formed with natural and deprotonated luteolin chelating bare and hydrated Cr(III) ion, respectively, are studied by using Density Functional Theory method. Both total and binding energies are calculated. The results from the studies indicate that Cr(III) ion is affine in forming a complex with luteolin at the 5-hydroxy-4-keto site and that deprotonated luteolin has stronger chelating power than natural luteolin. The reactivity differences between luteolin and luteolin-Cr(III) complexes are observed through comparison of their Conceptual DFT reactivity indices. Apart from the theoretical studies, the experiments are performed to modify the theoretical conclusions. Meanwhile, luteolin-Cr(III) complex has been synthesized, and the chelation site is analyzed using IR spectroscopy and UV/vis spectrum. The experimental results are found to have the same conclusions as those by theoretical studies.
Quantum-Chemical Calculations of Carbon-Isotope Fractionation in CO2(g), Aqueous Carbonate Species, and Carbonate Minerals
Rustad, James R.; Nelmes, Sierra L.; Jackson, Virgil E.; Dixon, David A.
Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of ~5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of ~0.5 per mil using ~10 solute-solvent conformations. The best results are obtained with the B3LYP/ aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework.
Quantum-chemical calculations of carbon-isotope fractionation in CO2(g), aqueous carbonate species, and carbonate minerals.
Rustad, James R; Nelmes, Sierra L; Jackson, Virgil E; Dixon, David A
Quantum chemical calculations on large supermolecular carbonate-water and carbonate mineral clusters are used to predict equilibrium constants for 13,12C-isotope-exchange reactions between CO2(g), aqueous carbonate species, and the common carbonate minerals. For the aqueous species, we evaluate the influence of the size and conformational variability of the solvation shell, the exchange-correlation functional, and the basis set. The choice of exchange-correlation functional (PBE vs B3LYP), the basis set (6-31G* vs aug-cc-pVDZ), and solvation shell size (first shell only vs first shell and a partial second shell) each produce changes of approximately 5-10 per mil in the reduced partition function ratio. Conformational variability gives rise to a standard error of approximately 0.5 per mil using approximately 10 solute-solvent conformations. The best results are obtained with the B3LYP/aug-cc-pVDZ combination, but because the improvements in the basis set and exchange correlation functional drive the reduced partition function ratios in opposite directions, reasonably good results are also obtained with the PBE/6-31G* combination. To construct molecular clusters representative of mineral environments, a new method is introduced on the basis of conservation of Pauling bond strength. Using these clusters as models for minerals, calculations of mineral-gas and mineral-aqueous carbon-isotope fractionation factors, are in good agreement with experimental measurements. Carbon-isotope fractionation factors for gas, aqueous, and mineral phases are thus integrated into a single theoretical/computational framework. PMID:18166027
Monte-Carlo calculation of the lateral Casimir forces between rectangular gratings within the formalism of lattice quantum field theory
Oleg Pavlovsky; Maxim Ulybyshev
We propose a new Monte-Carlo method for calculation of the Casimir forces. Our method is based on the formalism of noncompact lattice quantum electrodynamics. This approach has been tested in the simplest case of two ideal conducting planes. After this the method has been applied to the calculation of the lateral Casimir forces between two ideal conducting rectangular gratings. We compare our calculations with the results of PFA and "Optimal" PFA methods.
FragIt: A Tool to Prepare Input Files for Fragment Based Quantum Chemical Calculations
Steinmann, Casper; Ibsen, Mikael W.; Hansen, Anne S.; Jensen, Jan H.
Near linear scaling fragment based quantum chemical calculations are becoming increasingly popular for treating large systems with high accuracy and is an active field of research. However, it remains difficult to set up these calculations without expert knowledge. To facilitate the use of such methods, software tools need to be available to support these methods and help to set up reasonable input files which will lower the barrier of entry for usage by non-experts. Previous tools relies on specific annotations in structure files for automatic and successful fragmentation such as residues in PDB files. We present a general fragmentation methodology and accompanying tools called FragIt to help setup these calculations. FragIt uses the SMARTS language to locate chemically appropriate fragments in large structures and is applicable to fragmentation of any molecular system given suitable SMARTS patterns. We present SMARTS patterns of fragmentation for proteins, DNA and polysaccharides, specifically for D-galactopyranose for use in cyclodextrins. FragIt is used to prepare input files for the Fragment Molecular Orbital method in the GAMESS program package, but can be extended to other computational methods easily. PMID:23028546
Auxiliary-field quantum Monte Carlo calculations of molecular systems with a Gaussian basis.
Al-Saidi, W A; Zhang, Shiwei; Krakauer, Henry
We extend the recently introduced phaseless auxiliary-field quantum Monte Carlo (QMC) approach to any single-particle basis and apply it to molecular systems with Gaussian basis sets. QMC methods in general scale favorably with the system size as a low power. A QMC approach with auxiliary fields, in principle, allows an exact solution of the Schrodinger equation in the chosen basis. However, the well-known sign/phase problem causes the statistical noise to increase exponentially. The phaseless method controls this problem by constraining the paths in the auxiliary-field path integrals with an approximate phase condition that depends on a trial wave function. In the present calculations, the trial wave function is a single Slater determinant from a Hartree-Fock calculation. The calculated all-electron total energies show typical systematic errors of no more than a few millihartrees compared to exact results. At equilibrium geometries in the molecules we studied, this accuracy is roughly comparable to that of coupled cluster with single and double excitations and with noniterative triples [CCSD(T)]. For stretched bonds in H(2)O, our method exhibits a better overall accuracy and a more uniform behavior than CCSD(T). PMID:16784257
Characterising through Erasing: A Theoretical Framework for Representing Documents Inspired by Quantum Theory
┴lvaro Francisco Huertas-Rosero; Leif Azzopardi; C. J. van Rijsbergen
The problem of representing text documents within an Information Retrieval system is formulated as an analogy to the problem of representing the quantum states of a physical system. Lexical measurements of text are proposed as a way of representing documents which are akin to physical measurements on quantum states. Consequently, the representation of the text is only known after measurements have been made, and because the process of measuring may destroy parts of the text, the document is characterised through erasure. The mathematical foundations of such a quantum representation of text are provided in this position paper as a starting point for indexing and retrieval within a ``quantum like'' Information Retrieval system.
Theoretical study of dynamic electron-spin-polarization via the doublet-quartet quantum-mixed state and time-resolved ESR spectra of the quartet high-spin state.
Teki, Yoshio; Matsumoto, Takafumi
The mechanism of the unique dynamic electron polarization of the quartet (S = 3/2) high-spin state via a doublet-quartet quantum-mixed state and detail theoretical calculations of the population transfer are reported. By the photo-induced electron transfer, the quantum-mixed charge-separate state is generated in acceptor-donor-radical triad (A-D-R). This mechanism explains well the unique dynamic electron polarization of the quartet state of A-D-R. The generation of the selectively populated quantum-mixed state and its transfer to the strongly coupled pure quartet and doublet states have been treated both by a perturbation approach and by exact numerical calculations. The analytical solutions show that generation of the quantum-mixed states with the selective populations after de-coherence and/or accompanying the (complete) dephasing during the charge-recombination are essential for the unique dynamic electron polarization. Thus, the elimination of the quantum coherence (loss of the quantum information) is the key process for the population transfer from the quantum-mixed state to the quartet state. The generation of high-field polarization on the strongly coupled quartet state by the charge-recombination process can be explained by a polarization transfer from the quantum-mixed charge-separate state. Typical time-resolved ESR patterns of the quantum-mixed state and of the strongly coupled quartet state are simulated based on the generation mechanism of the dynamic electron polarization. The dependence of the spectral pattern of the quartet high-spin state has been clarified for the fine-structure tensor and the exchange interaction of the quantum-mixed state. The spectral pattern of the quartet state is not sensitive towards the fine-structure tensor of the quantum-mixed state, because this tensor contributes only as a perturbation in the population transfer to the spin-sublevels of the quartet state. Based on the stochastic Liouville equation, it is also discussed why the selective population in the quantum-mixed state is generated for the "finite field" spin-sublevels. The numerical calculations of the elimination of the quantum coherence (de-coherence and/or dephasing) are demonstrated. A new possibility of the enhanced intersystem crossing pathway in solution is also proposed. PMID:21321715
Accurate quantum dynamics calculations of vibrational spectrum of dideuteromethane CH2D2
NASA Astrophysics Data System (ADS)
Yu, Hua-Gen
We report a rigorous variational study of the infrared (IR) vibrational spectra of both CH2D2 and 13CH2D2 isotopomers using an exact molecular Hamiltonian. Calculations are carried out using a recently developed multi-layer Lanczos algorithm based on the accurate refined Wang and Carrington potential energy surface of methane and the low-order truncated ab initio dipole moment surface of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. All well converged 357 vibrational energy levels up to 6100 cm-1 of CH2D2 are obtained, together with a comparison to previous calculations and 91 experimental bands available. The calculated frequencies are in excellent agreement with the experimental results and give a root-mean-square error of 0.67 cm-1. In particular, we also compute the transition intensities from the vibrational ground state for both isotopomers. Based on the theoretical results, 20 experimental bands are suggested to be re-assigned. Surprisingly, an anomalous C isotopic effect is discovered in the n?5 modes of CH2D2. The predicted IR spectra provide useful information for understanding those unknown bands.
Crystal structure, spectroscopic investigations and quantum chemical calculational studies of N-diphenylphosphino-4-methylpiperidine sulfide
NASA Astrophysics Data System (ADS)
Sarańo?lu, Hanife; Sari÷z, ųzlem; ųznergiz, Sena
The title molecule, N-diphenylphosphino-4-methylpiperidine sulfide (I), has been synthesized and characterized by elemental analysis, 1H NMR, 31P NMR, IR and X-ray single-crystal determination. The molecular geometry from X-ray determination, vibrational frequencies and gauge, including atomic orbital (GIAO) 1H NMR and 31P NMR chemical shift values of the title compound (I) in the ground state have been calculated using the density functional theory with the 6-31G(d), 6-31G(d,p) and 6-311G(d,p) basis sets. The calculated results show that the optimized geometry can well reproduce the crystal structure, and theoretical vibrational frequencies and chemical shift values show good agreement with experimental values. The predicted nonlinear optical properties of the title compound are greater than those of urea. In addition, DFT calculations of the molecular electrostatic potentials, frontier molecular orbitals of the title compound were carried out at the B3LYP/6-31G(d) level of theory.
Accurate quantum dynamics calculations of vibrational spectrum of dideuteromethane CH2D2.
Yu, Hua-Gen
We report a rigorous variational study of the infrared (IR) vibrational spectra of both CH2D2 and (13)CH2D2 isotopomers using an exact molecular Hamiltonian. Calculations are carried out using a recently developed multi-layer Lanczos algorithm based on the accurate refined Wang and Carrington potential energy surface of methane and the low-order truncated ab initio dipole moment surface of Yurchenko et al. [J. Mol. Spectrosc. 291, 69 (2013)]. All well converged 357 vibrational energy levels up to 6100 cm(-1) of CH2D2 are obtained, together with a comparison to previous calculations and 91 experimental bands available. The calculated frequencies are in excellent agreement with the experimental results and give a root-mean-square error of 0.67?cm(-1). In particular, we also compute the transition intensities from the vibrational ground state for both isotopomers. Based on the theoretical results, 20 experimental bands are suggested to be re-assigned. Surprisingly, an anomalous C isotopic effect is discovered in the n?5 modes of CH2D2. The predicted IR spectra provide useful information for understanding those unknown bands. PMID:26001461
Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations.
Nagabalasubramanian, P B; Periandy, S; Karabacak, Mehmet; Govindarajan, M
The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100cm(-1). The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated. PMID:25795608
Molecular structure, vibrational, electronic and thermal properties of 4-vinylcyclohexene by quantum chemical calculations
NASA Astrophysics Data System (ADS)
Nagabalasubramanian, P. B.; Periandy, S.; Karabacak, Mehmet; Govindarajan, M.
The solid phase FT-IR and FT-Raman spectra of 4-vinylcyclohexene (abbreviated as 4-VCH) have been recorded in the region 4000-100 cm-1. The optimized molecular geometry and vibrational frequencies of the fundamental modes of 4-VCH have been precisely assigned and analyzed with the aid of structure optimizations and normal coordinate force field calculations based on density functional theory (DFT) method at 6-311++G(d,p) level basis set. The theoretical frequencies were properly scaled and compared with experimentally obtained FT-IR and FT-Raman spectra. Also, the effect due the substitution of vinyl group on the ring vibrational frequencies was analyzed and a detailed interpretation of the vibrational spectra of this compound has been made on the basis of the calculated total energy distribution (TED). The time dependent DFT (TD-DFT) method was employed to predict its electronic properties, such as electronic transitions by UV-Visible analysis, HOMO and LUMO energies, molecular electrostatic potential (MEP) and various global reactivity and selectivity descriptors (chemical hardness, chemical potential, softness, electrophilicity index). Stability of the molecule arising from hyper conjugative interaction, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Atomic charges obtained by Mulliken population analysis and NBO analysis are compared. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures are also calculated.
On the inclusion of prime factors to calculate the theoretical lower bounds in multiplierless single constant multiplications
NASA Astrophysics Data System (ADS)
Troncoso Romero, David E.; Meyer-Baese, Uwe; Dolecek, Gordana Jovanovic
This paper presents an extension to the theoretical lower bounds for the number of adders and for the adder depth in multiplierless single constant multiplications (SCM). It is shown that the number of prime factors of the constants is key information to extend the current lower bounds in certain cases that have not yet been exposed. Additionally, the hidden theoretical lower bound for the number of adders required to preserve the minimum adder depth is revealed.
Perspectives and Current the Development of Non-Born-Oppenheimer Atomic and Molecular Quantum Mechanical Variational Calculations using Explicitly Correlated Gaussian Basis Functions
NASA Astrophysics Data System (ADS)
Sharkey, Keeper L.; Adamowicz Team
The development of highly accurate theoretical quantum mechanics models for atomic and molecular calculations is crucial for the verification of the results of high-resolution experimental spectroscopy. High accuracy in the calculations can be achieved by not assuming the Born-Oppenheimer approximation (non-BO) and by using the variational principle. The non-relativistic Hamiltonian describing the internal state of the considered system used in the approach is obtained by separating out the center-of-mass motion from the laboratory frame Hamiltonian. The wave functions used in the calculations are expanded in terms of explicitly correlated Gaussian (ECG) functions. The optimization of the Gaussian non-linear parameters is aided by the analytical energy gradient determined with respect to these parameters. Examples of some very accurate calculations of small atoms and diatomic molecules will be presented. The presentation will also include a discussion of the extension of the approach to perform non-BO calculations of bound states of small triatomic molecules (e.g. H
Quantum-mechanical calculation of carrier distribution in MOS accumulation and strong inversion layers
Lee, Chien-Wei; Hwu, Jenn-Gwo [Graduate Institute of Electronics Engineering/ Department of Electrical Engineering, National Taiwan University, Taipei, 10617, Taiwan (China)] [Graduate Institute of Electronics Engineering/ Department of Electrical Engineering, National Taiwan University, Taipei, 10617, Taiwan (China)
We derive a statistical physics model of two-dimensional electron gas (2DEG) and propose an accurate approximation method for calculating the quantum-mechanical effects of metal-oxide-semiconductor (MOS) structure in accumulation and strong inversion regions. We use an exponential surface potential approximation in solving the quantization energy levels and derive the function of density of states in 2D to 3D transition region by applying uncertainty principle and Schr÷dinger equation in k-space. The simulation results show that our approximation method and theory of density of states solve the two major problems of previous researches: the non-negligible error caused by the linear potential approximation and the inconsistency of density of states and carrier distribution in 2D to 3D transition region.
Quantum three-body calculation of nonresonant triple-alpha reaction rate at low temperatures
Ogata, Kazuyuki; Kan, Masataka [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); RIKEN Nishina Center, Wako 351-0198 (Japan)
Triple-alpha reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the alpha-alpha nonresonant states significantly quenches the Coulomb barrier between the first two alpha-particles and the third alpha-particle. Consequently, the alpha-alpha nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-alpha reaction rate by 26 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.
Quantum three-body calculation of nonresonant triple-{alpha} reaction rate at low temperatures
Ogata, Kazuyuki; Kan, Masataka [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); Kamimura, Masayasu [Department of Physics, Kyushu University, Fukuoka 812-8581 (Japan); RIKEN Nishina Center, Wako 351-0198 (Japan)
Triple-{alpha} reaction rate is re-evaluated by directly solving the three-body Schroedinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. An accurate description of the {alpha}-{alpha} nonresonant states significantly quenches the Coulomb barrier between the first two {alpha}-particles and the third {alpha}-particle. Consequently, the{alpha}-{alpha} nonresonant continuum states give a markedly larger contribution at low temperatures than that reported in previous studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find an increase in triple-{alpha} reaction rate by about 20 orders of magnitude around 10{sup 7} K compared with the rate of NACRE.
Electronic properties of amino acid side chains: quantum mechanics calculation of substituent effects
Dwyer, Donard S
Background Electronic properties of amino acid side chains such as inductive and field effects have not been characterized in any detail. Quantum mechanics (QM) calculations and fundamental equations that account for substituent effects may provide insight into these important properties. PM3 analysis of electron distribution and polarizability was used to derive quantitative scales that describe steric factors, inductive effects, resonance effects, and field effects of amino acid side chains. Results These studies revealed that: (1) different semiempirical QM methods yield similar results for the electronic effects of side chain groups, (2) polarizability, which reflects molecular deformability, represents steric factors in electronic terms, and (3) inductive effects contribute to the propensity of an amino acid for ?-helices. Conclusion The data provide initial characterization of the substituent effects of amino acid side chains and suggest that these properties affect electron density along the peptide backbone. PMID:16078995
Nuclear quantum effects in chemical reactions via higher-order path-integral calculations
NASA Astrophysics Data System (ADS)
Engel, Hamutal; Eitan, Reuven; Azuri, Asaf; Major, Dan Thomas
A practical approach to treat nuclear quantum mechanical effects in simulations of condensed phases, such as enzymes, is via Feynman path integral (PI) formulations. Typically, the standard primitive approximation (PA) is employed in enzymatic PI simulations. Nonetheless, these PI simulations are computationally demanding due to the large number of beads required to obtain converged results. The efficiency of PI simulations may be greatly improved if higher-order factorizations of the density matrix operator are employed. Herein, we compare the results of model calculations obtained employing the standard PA, the improved operator of Takahashi and Imada (TI), and a gradient-based forward corrector algorithm due to Chin (CH). The quantum transmission coefficient is computed for the Eckart potential while the partition functions and rate constant are computed for the H2 + H hydrogen transfer reaction. These potentials are simple models for chemical reactions. The study of the different factorization methods reveals that in most cases the higher-order action converges faster than the PA and TI approaches, at a moderate computational cost.
Quantum noise in ring-laser gyros. I - Theoretical formulation of problem
J. D. Cresser; P. Meystre; W. Schleich; W. H. Louisell; M. O. Scully
The effects of quantum noise on the mean beat frequency and spectrum of laser gyroscopes is discussed, a general formulation of the problem is made from a quantum-noise perspective, and analytical results in various limits are obtained. The characteristic behavior of the beat signal in a conventional ring laser is summarized using a novel method that shows the characteristic locking
All information-theoretically secure key establishing protocols are quantum protocols
Mario Stipcevic
A theorem is proved which states that no classical key generating protocol could ever be provably secure. Consequently, candidates for provably secure protocols must rely on some quantum effect. Theorem relies on the fact that BB84 Quantum key distribution protocol has been proven secure.
Quantum Calculations on Salt Bridges with Water: Potentials, Structure, and Properties
Liao, Sing; Green, Michael E.
Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with a guanidinium basic group, the other lysine, which is a primary amine. Only arginine is modeled here, by ethyl guanidinium, while propionic acid is used as a model for either carboxylic acid. The salt bridges are accompanied by 0-12 water molecules; for each of the 13 systems, the energy-bond distance relation, natural bond orbitals (NBO), frequency calculations allowing thermodynamic corrections to room temperature, and dielectric constant dependence, were all calculated. The water molecules were found to arrange themselves in hydrogen bonded rings anchored to the oxygens of the salt bridge components. This was not surprising in itself, but it was found that the rings lead to a periodicity in the energy, and to a 'water addition' rule. The latter shows that the initial rings, with four oxygen atoms, become five member rings when an additional water molecule becomes available, with the additional water filling in at the bond with the lowest Wiberg index, as calculated using NBO. The dielectric constant dependence is the expected hyperbola, and the fit of the energy to the inverse dielectric constant is determined. There is an energy periodicity related to ring formation upon addition of water molecules. When 10 water molecules have been added, all spaces near the salt bridge are filled, completing the first hydration shell, and a second shell starts to form. The potentials associated with salt bridges depend on their hydration, and potentials assigned without regard to local hydration are likely to cause errors as large as or larger than kBT, thus suggesting a serious problem if these potentials are used in Molecular Dynamics simulations.
Quantum mechanical calculation of aqueuous uranium complexes: carbonate, phosphate, organic and biomolecular species
Kubicki, James D; Halada, Gary P; Jha, Prashant; Phillips, Brian L
Background Quantum mechanical calculations were performed on a variety of uranium species representing U(VI), U(V), U(IV), U-carbonates, U-phosphates, U-oxalates, U-catecholates, U-phosphodiesters, U-phosphorylated N-acetyl-glucosamine (NAG), and U-2-Keto-3-doxyoctanoate (KDO) with explicit solvation by H2O molecules. These models represent major U species in natural waters and complexes on bacterial surfaces. The model results are compared to observed EXAFS, IR, Raman and NMR spectra. Results Agreement between experiment and theory is acceptable in most cases, and the reasons for discrepancies are discussed. Calculated Gibbs free energies are used to constrain which configurations are most likely to be stable under circumneutral pH conditions. Reduction of U(VI) to U(IV) is examined for the U-carbonate and U-catechol complexes. Conclusion Results on the potential energy differences between U(V)- and U(IV)-carbonate complexes suggest that the cause of slower disproportionation in this system is electrostatic repulsion between UO2 [CO3]35- ions that must approach one another to form U(VI) and U(IV) rather than a change in thermodynamic stability. Calculations on U-catechol species are consistent with the observation that UO22+ can oxidize catechol and form quinone-like species. In addition, outer-sphere complexation is predicted to be the most stable for U-catechol interactions based on calculated energies and comparison to 13C NMR spectra. Outer-sphere complexes (i.e., ion pairs bridged by water molecules) are predicted to be comparable in Gibbs free energy to inner-sphere complexes for a model carboxylic acid. Complexation of uranyl to phosphorus-containing groups in extracellular polymeric substances is predicted to favor phosphonate groups, such as that found in phosphorylated NAG, rather than phosphodiesters, such as those in nucleic acids. PMID:19689800
Quantum and quasiclassical calculations on the OH+CO[r arrow]CO[sub 2]+H reaction
Clary, D.C. (Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW (United Kingdom)); Schatz, G.C. (Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (United States))
Scattering calculations on the OH+CO[r arrow]CO[sub 2]+H reaction are reported using both quantum and quasiclassical methods. The rotating bond approximation is used in the quantum calculations. This method explicitly treats the OH vibration and CO rotation in the reactants and the bending vibration and a local CO stretch in the CO[sub 2] product. Analogous quasiclassical trajectory computations are also reported. A potential energy surface obtained as a fit to [ital ab] [ital initio] data is used. The quantum reaction probabilities are dominated by sharp resonances corresponding to vibrationally excited states of the HOCO complex formed in the reaction. The quantum and quasiclassical lifetimes of these resonances compare quite well with measurements made by Wittig [ital et] [ital al]. Calculations of differential cross sections, rate coefficients, and CO[sub 2] vibrational product distributions are also compared with experimental data. The comparisons of quantum and quasiclassical calculations for models that treat explicitly different numbers of degrees of freedom provide detailed insight into the dynamics of the OH+CO reaction.
Comparison of polynomial approximations to speed up planewave-based quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Parker, William D.; Umrigar, C. J.; AlfĶ, Dario; Petruzielo, F. R.; Hennig, Richard G.; Wilkins, John W.
The computational cost of quantum Monte Carlo (QMC) calculations of realistic periodic systems depends strongly on the method of storing and evaluating the many-particle wave function. Previous work by Williamson et al. (2001) [35] and AlfĶ and Gillan, (2004) [36] has demonstrated the reduction of the O (N3) cost of evaluating the Slater determinant with planewaves to O (N2) using localized basis functions. We compare four polynomial approximations as basis functions - interpolating Lagrange polynomials, interpolating piecewise-polynomial-form (pp-) splines, and basis-form (B-) splines (interpolating and smoothing). All these basis functions provide a similar speedup relative to the planewave basis. The pp-splines have eight times the memory requirement of the other methods. To test the accuracy of the basis functions, we apply them to the ground state structures of Si, Al, and MgO. The polynomial approximations differ in accuracy most strongly for MgO, and smoothing B-splines most closely reproduce the planewave value for of the variational Monte Carlo energy. Using separate approximations for the Laplacian of the orbitals increases the accuracy sufficiently to justify the increased memory requirement, making smoothing B-splines, with separate approximation for the Laplacian, the preferred choice for approximating planewave-represented orbitals in QMC calculations.
Quantum-statistical line shape calculation for Lyman-? lines in dense H plasmas
NASA Astrophysics Data System (ADS)
Lorenzen, S.; Wierling, A.; Reinholz, H.; R÷pke, G.; Zammit, M. C.; Fursa, D. V.; Bray, I.
We present results for the Lyman-? line of hydrogen in dense plasmas. Full line profiles are calculated within a quantum-statistical method, based on thermodynamic Green's functions. The contributions of plasma ions and electrons are considered separately. Linear and quadratic Stark effect as well as quadrupole effects are taken into account for ions. The model microfield method is used to include ion dynamics. The focus of this work lies on the contribution to broadening and shift by free electrons beyond the Born approximation. The effect of strong collisions can be identified as ladder-like diagrams of the electron-emitter propagator. In an effective two-particle approximation, the electronic self-energy is given in terms of scattering amplitudes, analogous to Baranger's expressions [Baranger, M 1958 Phys. Rev. 112 855]. We obtained scattering amplitudes from convergent close-coupling calculations including medium effects via Debye screening. Additionally, the electronic coupling between initial and final states is taken care of by a vertex correction. In our examples, the free electron density ranges between 1023 and 1025 m-3 at a plasma temperature of 1 and 2 eV, respectively.
Accurate band gaps of semiconductors and insulators from Quantum Monte Carlo calculations
NASA Astrophysics Data System (ADS)
Nazarov, Roman; Hood, Randolph; Morales, Miguel
Ab initio calculations are useful tools in developing materials with targeted band gaps for semiconductor industry. Unfortunately, the main workhorse of ab initio calculations - density functional theory (DFT) in local density approximation (LDA) or generalized gradient approximation (GGA) underestimates band gaps. Several approaches have been proposed starting from empirical corrections to more elaborate exchange-correlation functionals to deal with this problem. But none of these work well for the entire range of semiconductors and insulators. Deficiencies of DFT as a mean field method can be overcome using many-body techniques. Quantum Monte Carlo (QMC) methods can obtain a nearly exact numerical solutions of both total energies and spectral properties. Diffusion Monte Carlo (DMC), the most widely used QMC method, has been shown to provide gold standard results for different material properties, including spectroscopic constants of dimers and clusters, equation of state for solids, accurate descriptions of defects in metals and insulators. To test DMC's accuracy in a wider range of semiconductors and insulators we have computed band gaps of several semiconductors and insulators. We show that DMC can provide superior agreement with experiment compared with more traditional DFT approaches including high level exchange-correlation functionals (e.g. HSE).
Accurate quantum dynamics calculations using symmetrized Gaussians on a doubly dense Von Neumann lattice.
Halverson, Thomas; Poirier, Bill
In a series of earlier articles [B. Poirier, J. Theor. Comput. Chem. 2, 65 (2003); B. Poirier and A. Salam, J. Chem. Phys. 121, 1690 (2004); and ibid. 121, 1704 (2004)], a new method was introduced for performing exact quantum dynamics calculations. The method uses a "weylet" basis set (orthogonalized Weyl-Heisenberg wavelets) combined with phase space truncation, to defeat the exponential scaling of CPU effort with system dimensionality--the first method ever able to achieve this long-standing goal. Here, we develop another such method, which uses a much more convenient basis of momentum-symmetrized Gaussians. Despite being non-orthogonal, symmetrized Gaussians are collectively local, allowing for effective phase space truncation. A dimension-independent code for computing energy eigenstates of both coupled and uncoupled systems has been created, exploiting massively parallel algorithms. Results are presented for model isotropic uncoupled harmonic oscillators and coupled anharmonic oscillators up to 27 dimensions. These are compared with the previous weylet calculations (uncoupled harmonic oscillators up to 15 dimensions), and found to be essentially just as efficient. Coupled system results are also compared to corresponding exact results obtained using a harmonic oscillator basis, and also to approximate results obtained using first-order perturbation theory up to the maximum dimensionality for which the latter may be feasibly obtained (four dimensions). PMID:23248981
Bethe-Salpeter and Quantum Monte Carlo Calculations of the Optical Properties of Carbon Fullerenes
NASA Astrophysics Data System (ADS)
Kent, P. R. C.; Tiago, M. L.; Reboredo, F. A.; Hood, Randolph Q.
We have calculated the low energy optical excitations of the carbon fullerenes C20, C24, C50, C60, C70, and C80. Properties are calculated via the GW-Bethe-Salpeter Equation (GW-BSE) and diffusion Quantum Monte Carlo (QMC) methods. We compare these approaches with time dependent density functional results and with experiment. GW-BSE and QMC have previously shown good agreement for small molecules, but this is the first study of these methods for these larger yet prototypical nanostructures. The first ionization potentials are consistently well reproduced and are similar for all the fullerenes and methods studied. However, electron affinities and first triplet exciton show substantial method and geometry dependence. GW-BSE yields triplet energies around 1eV below the QMC results. We discuss the possible reasons for these differences. Research at Oak Ridge National Laboratory performed at the Materials Science and Technology Division, sponsored by the Division of Materials Sciences, and at the Center for Nanophase Materials Sciences, sponsored by the Division of Scientific User Facilities, U.S. Department of Energy. Research at Lawrence Livermore National Laboratory was performed under Contract DE-AC52-07NA27344.
Experimental and theoretical study of optical properties and quantum size phenomena in the BiVO4/TiO2 nanostructures
NASA Astrophysics Data System (ADS)
Zalfani, M.; Mahdouani, M.; Bourguiga, R.; Su, B. L.
Novel BiVO4/3DOM TiO2 nanostructure has been synthesized by hydrothermal method. BiVO4 nanoparticles and TiO2 inverse opal structure have also been prepared as reference. The prepared samples were characterized by Diffuse reflectance UV-Visible and photoluminescence (PL) spectroscopy. The absorption spectra of BiVO4/TiO2 nanocomposite samples show an absorption edge in the visible region, suggesting the potential application of this composite as an active visible-light driven photocatalysts. Theoretically quantum confinement phenomena and size dependent optical properties of BiVO4 quantum dots have been also studied. Using the effective mass approximation model, we computed the optical properties for spherical BiVO4 nanoparticles incorporated in TiO2 matrix. The size dependent of charge carrier's energies were calculated. The result shows that the confinement energy decreases with increase the size of BiVO4 nanoparticles. Dielectric properties of the BiVO4 nanoparticles were investigated and it was found that the dielectric constant decreases significantly as the size is reduced as a result the exciton energy decreases. It has been also found that the radiative recombination lifetime is concurrently enhanced with decreasing BiVO4 QDs size.
Comment on: ōTheoretical calculation of turn-on delay time of VCSEL and effect of carriers recombinationö [Opt. Laser Technol. 39 (2007) 997-1001
NASA Astrophysics Data System (ADS)
Hisham, H. K.; Abas, A. F.; Mahdiraji, G. A.; Mahdi, M. A.; Muhammad Noor, A. S.
Zhang et al. [Opt. Laser Technol. 39 (2007) 997-1001], through theoretical calculation, have shown that the turn-on time delay can be reduced by increasing any of the non-radiative (Anr), radiative (B), and/or Auger recombination (C) coefficients at a constant injection current over threshold current. Here, we explain that the results presented by that paper are incorrect and the turn-on time delay increases by increasing any of the carrier recombination rate coefficients.
Vibrational dynamics of DNA. III. Molecular dynamics simulations of DNA in water and theoretical calculations of the two-dimensional vibrational spectra
Chewook Lee; Kwang-Hee Park; Jin-A. Kim; Seungsoo Hahn; Minhaeng Cho
A theoretical description of the vibrational excitons in DNA is presented by using the vibrational basis mode theory developed in Papers I and II. The parameters obtained from the density functional theory calculations, such as vibrational coupling constants and basis mode frequencies, are used to numerically simulate two-dimensional (2D) IR spectra of dGn:dCn and dAn:dTn double helices with n varying
Interfacial Atmospheric Chemistry: Quantum Chemical Calculations on the Mechanism of Protonation and Oligomerization of Isoprene on Aqueous Surfaces
NASA Astrophysics Data System (ADS)
Mishra, H.; Colussi, A. J.; Enami, S.; Nielsen, R. J.; Hoffmann, M. R.; Goddard, W. A.
It has become increasingly apparent that atmospheric chemistry involves more than gas-phase reactions. Key processes, such as the decay of NO2 in urban plumes and the associated daytime formation of HONO, and the rapid chemistries observed in and over forest canopies at nighttime defy explanation by conventional atmospheric chemistry mechanisms. We have recently reported experimental results on several gas-liquid reactions of atmospheric interest, such as the facile protonation of gaseous isoprene on mildly acidic (pH < 4) water. Although interfacial proton transfers, such as the one involved in the protonation of gaseous isoprene, also participate in cloud and ocean acidification, bioenergetics coupling, 'on-water' catalysis, self-assembly and molecular recognition, little is known about the molecular mechanisms of such reactions. Herein we apply quantum mechanics to investigate how biogenic or anthropogenic olefins may get protonated and undergo oligomerization at the air-water interface by performing model calculations on small water clusters carrying an excess proton as surrogates for the surface of mildly acidic water as sensed by gaseous isoprene (ISO). We find that ISO binds weakly to the surface of water and accepts a proton from H+(H2O)3, leading to ISOH+ via a proton transfer hindered by a ?G1ć = 5.6 kcal mol-1 kinetic barrier. Subsequently, another ISO attaches loosely to this ensemble, before being attacked by the ISOH+. This process, which represents the first step of the cationic polymerization of ISO, is hindered by a similar ?G2ć = 5.7 kcal mol-1 barrier. Our theoretical results are consistent with experimental (~ 10-4) uptake coefficients for ISO measured on acidic water.
Molecular structure of H-bonded complexes of N,N-diphenylformamidine studied by IR and NMR spectroscopy and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Bureiko, S. F.; Golubev, N. S.; Kucherov, S. Yu.; Shurukhina, A. V.
The results of experimental studies and theoretical calculations of vibrational frequencies and structure of H-bonded associates of N,N-diphenylformamidine and its complexes with carboxylic acids and hydrogen chloride in solution are discussed. The IR and low temperature NMR spectra show the existence of equilibrium between s-trans-monomers and cyclic dimers, such as cyclic H-bonded complexes with carboxylic acids in solution. The complexes with weak acids have molecular structure. The interaction with strong acids and hydrogen chloride results in formation of H-bonded ionic pairs with proton transfer to the N atom of the base. The results of quantum chemical calculations confirm the formation of cyclic molecular complexes with two H-bonds NHģO dbnd C and OHģN at the interaction with weak carboxylic acids; the proton transfer along the OHģN bridge was found for the complexes with stronger proton donors. The vibrational frequencies and intensities were obtained also by a version of variational multidimensional anharmonic calculations of vibrational electrooptic parameters in space of normal coordinates. It was shown that this approach is more preferable for calculating the high-frequency XH stretch in systems where the corresponding normal mode is less characteristic and involves motions of many atoms.
Protonation/deprotonation process of Emodin in aqueous solution and pKa determination: UV/Visible spectrophotometric titration and quantum/molecular mechanics calculations
NASA Astrophysics Data System (ADS)
da Cunha, Antonio R.; Duarte, Evandro L.; Lamy, M. Teresa; Coutinho, Kaline
We combined theoretical and experimental studies to elucidate the important deprotonation process of Emodin in water. We used the UV/Visible spectrophotometric titration curves to obtain its pKa values, pKa1 = 8.0 ▒ 0.1 and pKa2 = 10.9 ▒ 0.2. Additionally, we obtained the pKa values of Emodin in the water-methanol mixture (1:3v/v). We give a new interpretation of the experimental data, obtaining apparent pKa1 = 6.2 ▒ 0.1, pKa2 = 8.3 ▒ 0.1 and pKa3 > 12.7. Performing quantum mechanics calculations for all possible deprotonation sites and tautomeric isomers of Emodin in vacuum and in water, we identified the sites of the first and second deprotonation. We calculated the standard deprotonation free energy of Emodin in water and the pKa1, using an explicit model of the solvent, with Free Energy Perturbation theory in Monte Carlo simulations obtaining, ?Gaq = 12.1 ▒ 1.4 kcal/mol and pKa1 = 8.7 ▒ 0.9. With the polarizable continuum model for the solvent, we obtained ?Gaq = 11.6 ▒ 1.0 kcal/mol and pKa1 = 8.3 ▒ 0.7. Both solvent models gave theoretical results in very good agreement with the experimental values.
Intramolecular CH?? and CH?O interactions in the conformational stability of benzyl methyl ether studied by matrix-isolation infrared spectroscopy and theoretical calculations
NASA Astrophysics Data System (ADS)
Shin-ya, Kei; Takahashi, Osamu; Katsumoto, Yukiteru; Ohno, Keiichi
Contributions of the intramolecular CH⋯? and CH⋯O interactions to the molecular conformation of benzyl methyl ether (BME) have been investigated by matrix-isolation infrared (IR) spectroscopy combined with quantum chemical calculations. Comparative investigations have been carried out for propylbenzene. Quantum chemical calculations predict that there are two conformers for BME; for the ET conformer the methyl ether and the phenyl groups lie in the plane of the benzene ring, while for the AG conformer they are out of the plane. Comparison between the observed and calculated spectra for BME reveals that the ET and AG conformers coexist in an Ar matrix. By measuring matrix-isolation IR spectra of BME deposited at different gas temperatures, the enthalpy difference (? H (AG - ET)) between ET and AG conformers was determined to be -1.03 ▒ 0.06 kJ mol -1. The experimental and calculation results indicate that the AG conformer of BME is stabilized by the intramolecular CH⋯? and CH⋯O interactions.
Envelope function calculations of linear and nonlinear optical gains in a strained-layer quantum-well laser
Doyeol Ahn; Tae-Kyung Yoo
The linear and nonlinear optical gain of strained-layer InGaAs-AlGaAs quantum well (QW) lasers are studied theoretically, with band mixing effects taken into account. Effects of the biaxial compressive strain of the InGaAs-AlGaAs QW on the band structure are investigated by solving for the Pikus-Bir Hamiltonian. The biaxial compressive strain separates the HH and the LH subbands by pulling down the
Ab initio quantum Monte Carlo calculations of spin superexchange in cuprates: the benchmarking case of Ca2CuO3
Foyevtsova, Kateryna [ORNL] [ORNL; Krogel, Jaron T [ORNL] [ORNL; Kim, Jeongnim [ORNL] [ORNL; Kent, Paul R [ORNL] [ORNL; Dagotto, Elbio R [ORNL] [ORNL; Reboredo, Fernando A [ORNL] [ORNL
In view of the continuous theoretical efforts aimed at an accurate microscopic description of the strongly correlated transition metal oxides and related materials, we show that with continuum quantum Monte Carlo (QMC) calculations it is possible to obtain the value of the spin superexchange coupling constant of a copper oxide in a quantitatively excellent agreement with experiment. The variational nature of the QMC total energy allows us to identify the best trial wave function out of the available pool of wave functions, which makes the approach essentially free from adjustable parameters and thus truly ab initio. The present results on magnetic interactions suggest that QMC is capable of accurately describing ground state properties of strongly correlated materials.
Quantum mechanical calculation of the collision-induced absorption spectra of N2-N2 with anisotropic interactions
NASA Astrophysics Data System (ADS)
Karman, Tijs; Miliordos, Evangelos; Hunt, Katharine L. C.; Groenenboom, Gerrit C.; van der Avoird, Ad
We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling.
Quantum-chemical calculations and electron diffraction study of the equilibrium molecular structure of vitamin K3
NASA Astrophysics Data System (ADS)
Khaikin, L. S.; Tikhonov, D. S.; Grikina, O. E.; Rykov, A. N.; Stepanov, N. F.
The equilibrium molecular structure of 2-methyl-1,4-naphthoquinone (vitamin K3) having C s symmetry is experimentally characterized for the first time by means of gas-phase electron diffraction using quantum-chemical calculations and data on the vibrational spectra of related compounds.
Formation of NV centers in diamond: A theoretical study based on calculated transitions and migration of nitrogen and vacancy related defects
NASA Astrophysics Data System (ADS)
Deßk, Peter; Aradi, Bßlint; Kaviani, Moloud; Frauenheim, Thomas; Gali, Adam
Formation and excitation energies as well charge transition levels are determined for the substitutional nitrogen (Ns), the vacancy (V), and related point defects (NV, NVH, N2,N2V, and V2) by screened nonlocal hybrid density functional supercell plane wave calculations in bulk diamond. In addition, the activation energy for V and NV diffusion is calculated. We find good agreement between theory and experiment for the previously well-established data and predict missing ones. Based on the calculated properties of these defects, the formation of the negatively charged NV center is studied, because it is a prominent candidate for application in quantum information processing and for nanosensors. Our results indicate that NV defects are predominantly created directly by irradiation, while simultaneously produced vacancies will form V2 pairs during postirradiation annealing. Divacancies may pin the Fermi level, making the NV defects neutral.
Synthesis, characterization, and theoretical calculations of mononuclear copper(II) benzoate complex with 2-propylimidazole, [Cu(PIM) 2(PhCOO) 2
NASA Astrophysics Data System (ADS)
Peng, Xian; Cui, Guang-hua; Li, De-jie; Liu, Tong-fei
A mononuclear copper(II) complex, [Cu(PIM) 2(PhCOO) 2] ( 1) [where PIM = 2-propylimidazole] has been synthesized and characterized by elemental analysis, IR, UV-Vis, TGA, and single crystal X-ray diffraction. The structural analysis indicated that Cu(II) atom in the complex is six-coordinated in a distorted octahedral geometry by two N atoms from two 2-propylimidazole and four O atoms from two benzoate ligands. In addition, based on crystal structural data, quantum chemistry calculation in DFT/B3LYP level has been used to reoptimize and explore the electronic structure of the compound 1; time-dependent DFT (TD-DFT) calculations have also been performed in order to elucidate its spectroscopic properties. All parameters from the calculations are in well accordance with our experimental result.
W G Unruh
Quantum mechanics is one of the most successful theoretical structures in all of science. Developed between 1925-26 to explain the optical spectrum of atoms, the theory over the succeeding 80 years has been extended, first to quantum field theories, gauge field theories, and now even string theory. It is used every day by thousands of physicists to calculate physical phenomena
Atomistic and Nanoscale Origins of Macroscopic Properties of Silicate Melts at High-Pressure: Spectroscopy & Quantum Chemical Calculations
NASA Astrophysics Data System (ADS)
Lee, S.; Fei, Y.; Cody, G.; Mysen, B.; Mao, H.; Eng, P.
Atomic structure of amorphous oxide melts at high pressure controls their macroscopic properties and geophysical progresses in the Earth's interior. Advances in NMR spectroscopy, x-ray optics, and theoretical analyses enable us to determine the structure of silicate glasses and provides clues to the microscopic origins of melt properties and relevant geochemical processes, such as generation, migration, and dynamics of magmas at high pressures (e.g. Lee et al. Geophy. Res. Letts. 2003, 30, p1845; Lee et al. Phys. Rev. Letts. 2005, 94, p165507; Lee et al. Nature Materials 2005, accepted). Here we report recent progress on pressure-induced structural changes in various amorphous oxide glasses and melt at high pressures using multi-nuclear solid state NMR, and synchrotron X-rays, and quantum simulations. In prototypical amorphous borates, and silicates, as well as complex aluminosilicate glasses and melts, the fractions of highly coordinated framework units (e.g. five coordinated [5,6]Si, [5,6]Al, [4]B) increase with increasing pressure with multiple densification mechanisms. The distribution of these framework cations at high pressure is not completely random but favors formation of oxygen linking dissimilar Si pairs such as [5,6]Si-O-[4]Al. Whereas the general trend in the effect of pressure on the structure is similar in those amorphous oxides, detailed pressure-induced structural changes are largely dependent on the degree of polymerization in the melts, types and fractions of network modifying cations at isobaric conditions. Topological disorder due to Si-O bond length distribution increases with pressure and is also larger for more polymerized amorphous oxides. Na-23 NMR spectra for sodium silicate and aluminosilicate glasses revealed that Na-O distance in the binary sodium silicates increases with pressure but that in the aluminosilicate glasses decreases with pressure. These results demonstrate that the pressure-induced structural changes in the silicate melts at high pressure and the corresponding changes in properties are complex function of composition. Pressure dependence of thermodynamics and transport properties such as diffusivity and viscosity of melts were directly calculated from experimentally measured atomic-scale disorder, and from variation of non-bridging oxygen fraction with pressure from spectroscopic data. These calculation results suggest that non-linear pressure dependence of viscosity of silicate melts stems from both the isobaric NBO fraction and its pressure dependence, yielding improved prospects for understanding the atomistic origins of magmatic processes in Earth's interior.
Direct calculation of the reactive transition matrix by L-squared quantum mechanical variational methods with complex boundary conditions
NASA Technical Reports Server (NTRS)
Sun, Yan; Yu, Chin-Hui; Kouri, Donald J.; Schwenke, David W.; Halvick, Philippe
A new formalism of the generalized Newton variational principle for the calculation of quantum mechanical state-to-state reaction probabilities is presented. The reformulation involves solving directly for the transition matrix rather than the reactance mtrix so that calculations may be carried out for individual columns of the transition matrix without obtaining solutions for all possible initial channels. The convergence of calculations with real and complex boundary conditions are compared for H + H2 - H2 + H, O + H2 - OH + H, and O + HD - OH + D and OD + H.
Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling.
Busch, Anna; Gonzßlez-GarcĒa, N·ria; Lendvay, Gy÷rgy; Olzmann, Matthias
The thermal decomposition of cyanonitrene, NCN, was studied behind reflected shock waves in the temperature range 1790-2960 K at pressures near 1 and 4 bar. Highly diluted mixtures of NCN3 in argon were shock-heated to produce NCN, and concentration-time profiles of C atoms as reaction product were monitored with atomic resonance absorption spectroscopy at 156.1 nm. Calibration was performed with methane pyrolysis experiments. Rate coefficients for the reaction (3)NCN + M ? (3)C + N2 + M (R1) were determined from the initial slopes of the C atom concentration-time profiles. Reaction R1 was found to be in the low-pressure regime at the conditions of the experiments. The temperature dependence of the bimolecular rate coefficient can be expressed with the following Arrhenius equation: k1(bim) = (4.2 ▒ 2.1) ū 10(14) exp[-242.3 kJ mol(-1)/(RT)] cm(3) mol(-1) s(-1). The rate coefficients were analyzed by using a master equation with specific rate coefficients from RRKM theory. The necessary molecular data and energies were calculated with quantum chemical methods up to the CCSD(T)/CBS//CCSD/cc-pVTZ level of theory. From the topography of the potential energy surface, it follows that reaction R1 proceeds via isomerization of NCN to CNN and subsequent C-N bond fission along a collinear reaction coordinate without a tight transition state. The calculations reproduce the magnitude and temperature dependence of the rate coefficient and confirm that reaction R1 is in the low-pressure regime under our experimental conditions. PMID:25853321
Theoretical Calculation of the Power Spectra of the Rolling and Yawing Moments on a Wing in Random Turbulence
NASA Technical Reports Server (NTRS)
Eggleston, John M; Diederich, Franklin W
The correlation functions and power spectra of the rolling and yawing moments on an airplane wing due to the three components of continuous random turbulence are calculated. The rolling moments to the longitudinal (horizontal) and normal (vertical) components depend on the spanwise distributions of instantaneous gust intensity, which are taken into account by using the inherent properties of symmetry of isotropic turbulence. The results consist of expressions for correlation functions or spectra of the rolling moment in terms of the point correlation functions of the two components of turbulence. Specific numerical calculations are made for a pair of correlation functions given by simple analytic expressions which fit available experimental data quite well. Calculations are made for four lift distributions. Comparison is made with the results of previous analyses which assumed random turbulence along the flight path and linear variations of gust velocity across the span.
Path integral calculation of thermal rate constants within the quantum instanton approximation: Application to the HCH4\\H2CH3 hydrogen
Miller, William H.
Yamamoto, and William H. Millera) Department of Chemistry and Kenneth S. Pitzer Center for Theoretical and recalibrated version of the JordanŁ Gilbert potential surface. The quantum instanton rate is evaluated using
Accurate experimental and theoretical comparisons between superconductor-insulator-superconductor mixers showing weak and strong quantum effects
NASA Technical Reports Server (NTRS)
Mcgrath, W. R.; Richards, P. L.; Face, D. W.; Prober, D. E.; Lloyd, F. L.
A systematic study of the gain and noise in superconductor-insulator-superconductor mixers employing Ta based, Nb based, and Pb-alloy based tunnel junctions was made. These junctions displayed both weak and strong quantum effects at a signal frequency of 33 GHz. The effects of energy gap sharpness and subgap current were investigated and are quantitatively related to mixer performance. Detailed comparisons are made of the mixing results with the predictions of a three-port model approximation to the Tucker theory. Mixer performance was measured with a novel test apparatus which is accurate enough to allow for the first quantitative tests of theoretical noise predictions. It is found that the three-port model of the Tucker theory underestimates the mixer noise temperature by a factor of about 2 for all of the mixers. In addition, predicted values of available mixer gain are in reasonable agreement with experiment when quantum effects are weak. However, as quantum effects become strong, the predicted available gain diverges to infinity, which is in sharp contrast to the experimental results. Predictions of coupled gain do not always show such divergences.
Line coupling effects in the isotropic Raman spectra of N2: A quantum calculation at room temperature
NASA Astrophysics Data System (ADS)
Thibault, Franck; Boulet, Christian; Ma, Qiancheng
We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10 200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.
Line Coupling Effects in the Isotropic Raman Spectra of N2: A Quantum Calculation at Room Temperature
NASA Technical Reports Server (NTRS)
Thibault, Franck; Boulet, Christian; Ma, Qiancheng
We present quantum calculations of the relaxation matrix for the Q branch of N2 at room temperature using a recently proposed N2-N2 rigid rotor potential. Close coupling calculations were complemented by coupled states studies at high energies and provide about 10200 two-body state-to state cross sections from which the needed one-body cross-sections may be obtained. For such temperatures, convergence has to be thoroughly analyzed since such conditions are close to the limit of current computational feasibility. This has been done using complementary calculations based on the energy corrected sudden formalism. Agreement of these quantum predictions with experimental data is good, but the main goal of this work is to provide a benchmark relaxation matrix for testing more approximate methods which remain of a great utility for complex molecular systems at room (and higher) temperatures.
Properties of Solar Thermal Fuels by Accurate Quantum Monte Carlo Calculations
NASA Astrophysics Data System (ADS)
Saritas, Kayahan; Ataca, Can; Grossman, Jeffrey C.
Efficient utilization of the sun as a renewable and clean energy source is one of the major goals of this century due to increasing energy demand and environmental impact. Solar thermal fuels are materials that capture and store the sun's energy in the form of chemical bonds, which can then be released as heat on demand and charged again. Previous work on solar thermal fuels faced challenges related to the cyclability of the fuel over time, as well as the need for higher energy densities. Recently, it was shown that by templating photoswitches onto carbon nanostructures, both high energy density as well as high stability can be achieved. In this work, we explore alternative molecules to azobenzene in such a nano-templated system. We employ the highly accurate quantum Monte Carlo (QMC) method to predict the energy storage potential for each molecule. Our calculations show that in many cases the level of accuracy provided by density functional theory (DFT) is sufficient. However, in some cases, such as dihydroazulene, the drastic change in conjugation upon light absorption causes the DFT predictions to be inconsistent and incorrect. For this case, we compare our QMC results for the geometric structure, band gap and reaction enthalpy with different DFT functionals.
Schwarzschild Radius from Monte Carlo Calculation of the Wilson Loop in Supersymmetric Matrix Quantum Mechanics
Hanada, Masanori [Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Miwa, Akitsugu [Institute of Physics, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902 (Japan); Harish-Chandra Research Institute, Chhatnag Road, Jhunsi, Allahabad 211019 (India); Nishimura, Jun [High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801 (Japan); Department of Particle and Nuclear Physics, School of High Energy Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), Tsukuba 305-0801 (Japan); Takeuchi, Shingo [Department of Particle and Nuclear Physics, School of High Energy Accelerator Science, Graduate University for Advanced Studies (SOKENDAI), Tsukuba 305-0801 (Japan); Asia Pacific Center for Theoretical Physics (APCTP), Pohang, Gyeongbuk 790-784 (Korea, Republic of)
In the string-gauge duality it is important to understand how the space-time geometry is encoded in gauge theory observables. We address this issue in the case of the D0-brane system at finite temperature T. Based on the duality, the temporal Wilson loop W in gauge theory is expected to contain the information of the Schwarzschild radius R{sub Sch} of the dual black hole geometry as log
On the Systematic Error in the Quantum Mechanical Calculations to the Periodic Table of Elements
NASA Astrophysics Data System (ADS)
Khazan, Albert
The scientists working on the problems of the Periodic Table of Elements regularly attempt to create models of the elements on the basis of the laws of Quantum Mechanics. One even attempted to use the calculation of the dependency ``atomic mass - element's number'' on this basis, in order to extend the Table by introducing two new Periods containing 50 elements each. The hyperbolic law we have found in the Periodic Table allows to find, first, the atomic mass of the last (heaviest stable) element (411.66), then - the number of the protons in it (155). Two functions were compared: the IUPAC 2007 function (elements 80-118) and another one created according the other data (elements 80-224). Both functions have a large deviation of data in No.104-118. Commencing in Period 8, there are three ``shifts'' of atomic mass for 17, 20, and 25 AMU. Also, our analysis manifests that there in all the aforementioned data is a single point with atomic mass 412 and number 155, where the parameters meet each other. This fact verifies our theory (Khazan A. Upper Limit in Mendeleev's Periodic Table - Element No.155. 2nd ed., Svenska fysikarkivet, Stockholm, 2010).
Humic Acid Metal Cation Interaction Studied by Spectromicroscopy Techniques in Combination with Quantum Chemical Calculations
Plaschke, M.; Rothe, J; Armbruster, M; Denecke, M; Naber, A; Geckeis, H
Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)-HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K-edge and laser scanning luminescence microscopy (LSLM) at the {sup 5}D{sub 0} {yields} {sup 7}F{sub 1,2} fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s-NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)-HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a 'pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material.
Leading-order calculation of electric conductivity in hot quantum electrodynamics from diagrammatic methods
Gagnon, Jean-Sebastien; Jeon, Sangyong [Physics Department, McGill University, 3600 University street, Montreal, H3A 2T8 (Canada)
Using diagrammatic methods, we show how the Ward identity can be used to constrain the ladder kernel in transport coefficient calculations. More specifically, we use the Ward identity to determine the necessary diagrams that must be resummed using an integral equation. One of our main results is an equation relating the kernel of the integral equation with functional derivatives of the full self-energy; it is similar to what is obtained with two-particle irreducible (2PI) effective action methods. However, since we use the Ward identity as our starting point, gauge invariance is preserved. Using power counting arguments, we also show which self-energies must be included in the resummation at leading order, including 2 to 2 scatterings and 1 to 2 collinear scatterings with the Landau-Pomeranchuk-Migdal effect. We show that our quantum field theory result is equivalent to the one of Arnold, Moore, and Yaffe obtained using effective kinetic theory. In this paper we restrict our discussion to electrical conductivity in hot QED, but our method can in principle be generalized to other transport coefficients and other theories.
Elucidating triplet-sensitized photolysis mechanisms of sulfadiazine and metal ions effects by quantum chemical calculations.
Wang, Se; Song, Xuedan; Hao, Ce; Gao, Zhanxian; Chen, Jingwen; Qiu, Jieshan
Sulfadiazine (SDZ) mainly proceeds triplet-sensitized photolysis with dissolved organic matter (DOM) in the aquatic environment. However, the mechanisms underlying the triplet-sensitized photolysis of SDZ with DOM have not been fully worked out. In this study, we investigated the mechanisms of triplet-sensitized photolysis of SDZ(0) (neutral form) and SDZ(-) (anionic form) with four DOM analogues, i.e., fluorenone (FL), thioxanthone (TX), 2-acetonaphthone (2-AN), and 4-benzoylbenzoic acid (CBBP), and three metal ions (i.e., Mg(2+), Ca(2+), and Zn(2+)) effects using quantum chemical calculations. Results indicated that the triplet-sensitized photolysis mechanism of SDZ(0) with FL, TX, and 2-AN was hydrogen transfer, and with CBBP was electron transfer along with proton transfer (for complex SDZ(0)-CBBP2) and hydrogen transfer (for complex SDZ(0)-CBBP1). The triplet-sensitized photolysis mechanisms of SDZ(-) with FL, TX, and CBBP was electron transfer along with proton transfer, and with 2-AN was hydrogen transfer. The triplet-sensitized photolysis product of both SDZ(0) and SDZ(-) was a sulfur dioxide extrusion product (4-(2-iminopyrimidine-1(2H)-yl)aniline), but the formation routs of the products for SDZ(0) and SDZ(-) were different. In addition, effects of the metal ions on the triplet-sensitized photolysis of SDZ(0) and SDZ(-) were different. The metal ions promoted the triplet-sensitized photolysis of SDZ(0), but inhibited the triplet-sensitized photolysis of SDZ(-). PMID:25496743
The Impact of Quantum Theoretical Models of Consciousness on the Study of Education.
ERIC Educational Resources Information Center
Andris, James F.
This paper abstracts and discusses the approaches of five educational theorists who have used quantum theory as a model for educational phenomena, sets forth and uses metatheoretical criteria to evaluate the work of these theorists, and states guidelines for further work in this domain. The paper abstracts and discusses the works of the followingģ
Vapor-phase Raman spectra, theoretical calculations, and the vibrational and structural properties of cis- and trans-stilbene.
Egawa, Toru; Shinashi, Kiyoaki; Ueda, Toyotoshi; Ocola, Esther J; Chiang, Whe-Yi; Laane, Jaan
The vapor-phase Raman spectra of cis- and trans-stilbene have been collected at high temperatures and assigned. The low-frequency skeletal modes were of special interest. The molecular structures and vibrational frequencies of both molecules have also been obtained using MP2/cc-pVTZ and B3LYP/cc-pVTZ calculations, respectively. The two-dimensional potential map for the internal rotations around the two Cphenyl-C(?C) bonds of cis-stilbene was generated by using a series of B3LYP/cc-pVTZ calculations. It was confirmed that the molecule has only one conformer with C2 symmetry. The energy level calculation with a two-dimensional Hamiltonian was carried out, and the probability distribution for each level was obtained. The calculation revealed that the "gearing" internal rotation in which the two phenyl rings rotate with opposite directions has a vibrational frequency of 26 cm(-1), whereas that of the "antigearing" internal rotation in which the phenyl rings rotate with the same direction is about 52 cm(-1). In the low vibrational energy region the probability distribution for the gearing internal rotation is similar to that of a one-dimensional harmonic oscillator, and in the higher region the motion behaves like that of a free rotor. PMID:24409818
Nonperturbative quantum and classical calculations of multiphoton vibrational excitation and dissociation of Morse molecules^1
NASA Astrophysics Data System (ADS)
Dimitriou, K. I.; Mercouris, Th.; Constantoudis, V.; Komninos, Y.; Nicolaides, C. A.
The multiphoton vibrational excitation and dissociation of Morse molecules have been computed nonperturbatively using Hamilton's and Schr?dinger's time-dependent equations, for a range of laser pulse parameters. The time-dependent Schr?dinger equation is solved by the state-specific expansion approach [e.g.,1]. For its solution, emphasis has been given on the inclusion of the continuous spectrum, whose contribution to the multiphoton probabilities for resonance excitation to a number of excited discrete states as well as to dissociation has been examined as a function of laser intensity, frequency and pulse duration. An analysis of possible quantal-classical correspondences for this system is being carried out. We note that distinct features exist from previous classical calculations [2]. For example, the dependence on the laser frequency gives rise to an asymmetry around the red-shifted frequency corresponding to the maximum probability. [1] Th. Mercouris, I. D. Petsalakis and C. A. Nicolaides, J. Phys. B 27, L519 (1994). [2] V. Constantoudis and C. A. Nicolaides, Phys. Rev. E 64, 562112 (2001). ^1This work was supported by the program 'Pythagoras' which is co - funded by the European Social Fund (75%) and Natl. Resources (25%). ^2Physics Department, National Technical University, Athens, Greece.^3Theoretical and Physical Chemistry Institute, Hellenic Research Foundation, Athens, Greece.
Quantum entanglement phenomena in photosynthetic light harvesting complexes
K. Birgitta Whaley; Mohan Sarovar; Akihito Ishizaki
We review recent theoretical calculations of quantum entanglement in photosynthetic light harvesting complexes. These works establish, for the first time, a manifestation of this characteristically quantum mechanical phenomenon in biologically functional structures. We begin by summarizing calculations on model biomolecular systems that aim to reveal non-trivial characteristics of quantum entanglement in non-equilibrium biological environments. We then discuss and compare several
Quantum entanglement phenomena in photosynthetic light harvesting complexes
K. Birgitta Whaley; Mohan Sarovar; Akihito Ishizaki
We review recent theoretical calculations of quantum entanglement in photosynthetic light harvesting complexes. These works establish, for the first time, a manifestation of this characteristically quantum mechanical phenomenon in biologically functional structures. We begin by summarizing calculations on model biomolecular systems that aim to reveal non-trivial characteristics of quantum entanglement in non-equilibrium biological environments. We then discuss and compare several
Efficiency enhancement calculations of state-of-the-art solar cells by luminescent layers with spectral shifting, quantum cutting, and quantum tripling function
NASA Astrophysics Data System (ADS)
ten Kate, O. M.; de Jong, M.; Hintzen, H. T.; van der Kolk, E.
Solar cells of which the efficiency is not limited by the Shockley-Queisser limit can be obtained by integrating a luminescent spectral conversion layer into the cell structure. We have calculated the maximum efficiency of state-of-the-art c-Si, pc-Si, a-Si, CdTe, GaAs, CIS, CIGS, CGS, GaSb, and Ge solar cells with and without an integrated spectral shifting, quantum cutting, or quantum tripling layer using their measured internal quantum efficiency (IQE) curves. Our detailed balance limit calculations not only take into account light in-coupling efficiency of the direct AM1.5 spectral irradiance but also wavelength dependence of the refractive index and the IQEs of the cells and the angular dependent light in-coupling of the indirect spectral irradiance. An ideal quantum cutting layer enhances all cell efficiencies ranging from a modest 2.9% for c-Si to much larger values of 4.0%, 7.7%, and 11.2% for CIGS, Ge, and GaSb, respectively. A quantum tripling layer also enhances cell efficiencies, but to a lesser extent. These efficiency enhancements are largest for small band gap cells like GaSb (7.5%) and Ge (3.8%). Combining a quantum tripling and a quantum cutting layer would enhance efficiency of these cells by a factor of two. Efficiency enhancement by a simple spectral shifting layer is limited to less than 1% in case the IQE is high for blue and UV lights. However, for CdTe and GaSb solar cells, efficiency enhancements are as high as 4.6% and 3.5%, respectively. A shifting layer based on available red LED phosphors like Sr2Si5N8:Eu will raise CdTe efficiency by 3.0%.
Elementary Surface Reaction Simulation of Aluminum Chemical Vapor Deposition from Dimethylaluminumhydride Based on Ab Initio Calculations: Theoretical Process Optimization Procedure (2)
NASA Astrophysics Data System (ADS)
Sugiyama, Masakazu; Nakajima, Tohru; Tanaka, Takeo; Itoh, Hitoshi; Aoyama, Jyun-ichi; Egashira, Yasuyuki; Yamashita, Kohichi; Komiyama, Hiroshi; Shimogaki, Yukihiro
This work demonstrates how to develop a qualitative surface reaction model to an elementary surface reaction simulation of deposition for the quantitative examination of model validity. Chemical vapor deposition of Al (Al-CVD) from dimethylaluminumhydride (DMAH) is examined as an example of this method. The surface reaction model of DMAH was deduced from ab initio cluster model calculations and experimental measurements of reaction products. Rate constants of all the elementary reactions were estimated for an elementary reaction model. Transition-state theory enabled the calculation of rate constants using the activation energies obtained from ab initio calculations. Entropy terms, however, were estimated by using an empirical method to reduce the computational effort. This approach minimized the ab initio calculations required to form a reaction data set. Simulated deposition profiles were compared with experimental data for Al-CVD in a tube reactor. Good agreement between the results of simulations and experiments indicate the possibility of constructing surface-reaction data sets for CVD process simulations based on ab initio quantum-chemical calculations.
A theoretical study on storage states of Li ions in carbon anodes of Li ion batteries using molecular orbital calculations
Tetsuo Suzuki; Takahiro Hasegawa; Shin R. Mukai; Hajime Tamon
Semi-empirical molecular orbital calculations were carried out to clarify storage states of Li ions in amorphous carbon anodes of Li ion batteries. Storage states of Li ions between two graphene sheets were investigated and a favorable structure for a carbon anode to produce large reversible and small irreversible capacities is discussed. A polycyclic hydrocarbon molecule, C54H18, was used as a
Theoretical studies of H2-H2 collisions. V - Ab initio calculations of relaxation phenomena in parahydrogen gas
W. E. Koehler; J. Schaefer
The temperature dependence of effective Waldmann¢Snider cross sections determining relaxation and line broadening phenomena has been studied for p-H2 between 20 and 200 K. In particular, the rotational relaxation cross section and the relaxation cross sections of the rotational angular momentum vector and tensor polarizations and their respective fluxes have been calculated in an entirely ab initio treatment and close
DETERMINATION OF IONIZATION ENERGIES OF C {sub n} N (n = 4-12): VACUUM ULTRAVIOLET PHOTOIONIZATION EXPERIMENTS AND THEORETICAL CALCULATIONS
Oleg Kostko; Zhou Jia; Musahid Ahmed; Bian Jian Sun; Jie Shiuan Lie; Agnes H. H. Chang; Ralf I. Kaiser
Results from single photon vacuum ultraviolet photoionization of astrophysically relevant C{sub n} N clusters, n = 4-12, in the photon energy range of 8.0 eV-12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the C{sub n} N species. A search through numerous nitrogen-terminated C{sub n} N isomers for n =
Determination of Ionization Energies of CnN (n = 4-12): Vacuum Ultraviolet Photoionization Experiments and Theoretical Calculations
Oleg Kostko; Jia Zhou; Bian Jian Sun; Jie Shiuan Lie; Agnes H. H. Chang; Ralf I. Kaiser; Musahid Ahmed
Results from single photon vacuum ultraviolet photoionization of astrophysically relevant C n N clusters, n = 4-12, in the photon energy range of 8.0 eV-12.8 eV are presented. The experimental photoionization efficiency curves, combined with electronic structure calculations, provide improved ionization energies of the C n N species. A search through numerous nitrogen-terminated C n N isomers for n =
Calculational and experimental investigations of void effect -- A simple theoretical model for space-dependent leakage treatment of heterogeneous assemblies
Benoist, P.; Petrovic, I. (Commissariat a' l'Energie Atomique, Gif-sur-Yvette (France)); Mondot, J. (Commissariat a l'Energie Atomique, Saint Paul lez Durance (France))
This method, which takes into account the influence of assembly heterogeneity on neutron leakage, is based on the heterogeneous B[sub 1] formalism, which assumes the existence of a fundamental mode in an infinite and regular lattice of heterogeneous assemblies. A simplified formalism, TIBERE, is presented that allows one to define directional space-dependent leakage coefficients. This method, introduced for two-dimensional x-y geometry in the APOLLO-2 multigroup transport code, uses classical and directional first-flight collision probabilities. One can now define leakage cross sections as additional absorption cross sections that have space and energy dependence, as well as all other cross sections. Hence, one obtains perfectly consistent reaction and leakage rates used in an equivalence procedure, determining cell-homogenized parameters for a whole core calculation. The study of this refined heterogeneous leakage treatment was undertaken because of the insufficiency of the homogeneous leakage model, especially in cases when an assembly contain voided zones or almost voided zones, i.e., zones with a long mean free path, so that the streaming effect may become important. The fission rate comparison between the EPICURE reactor experimental results and the results of the corresponding whole reactor calculations were accomplished, with leakages calculated by the homogeneous and the TIBERE procedures of the APOLLO-2 code.
NMR spectroscopy and theoretical calculations in the conformational analysis of 1-methylpyrrolidin-2-one 3-halo-derivatives.
de Melo, Ulisses Zonta; Silva, RaĒ G M; Yamazaki, Diego A S; Pontes, Rodrigo M; Gauze, Gisele F; Rosa, Fernanda A; Rittner, Roberto; Basso, Ernani A
This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)J(HH) experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O?C-N-R bond, with C4 forming the "envelope lid". When the conformation changes, the "lid" alternates between positions above and below the amide plane. The ?-carbonyl halogen assumes two positions: a pseudo-axial and a pseudo-equatorial. In the gaseous phase, the calculations indicate that the pseudo-axial conformer is more stable and preferable going down the halogen family. Natural bond orbital analysis showed that electronic delocalization is significant only for the iodo derivative. In the other derivatives, the electrostatic repulsion between oxygen and the halogen determines the conformational equilibrium. When the solvated molecule was taken into account, the pseudo-equatorial conformer population increased with the relative permittivity of the solvent. This variation was strong in the fluoro derivative, and the preference was inverted. In the chlorine derivative, the two populations became closer in methanol and acetonitrile. In the bromine and iodine derivatives, the percentage of pseudo-equatorial conformer increased only slightly owing to the dipole moment of the conformation: the pseudo-equatorial conformation has a greater dipole moment and thus is stable in media with high relative permittivity. PMID:25679501
Comparison of quantum, semi-classical and classical methods in the calculation of nitrogen self-broadened linewidths
NASA Astrophysics Data System (ADS)
Thibault, Franck; Gomez, Laura; Ivanov, Sergey V.; Buzykin, Oleg G.; Boulet, Christian
We perform dynamical calculations on two robust N2-N2 potential energy surfaces in order to intercompare pressure broadening coefficients derived from close coupling and coupled states quantum dynamical methods, the semi-classical model of Robert and Bonamy and a full classical method. The coupled states and full classical results compare well with the experimental results or with close coupling values when available. This study confirms that the classical method is a good alternative at room and high temperatures to quantum dynamical methods. The results obtained using the semi-classical method however deviate from the other sets of data at all temperatures considered here (77-2400 K).
Capturing and Analyzing the Excited-State Structure of a Cu(I) Phenanthroline Complex by Time-Resolved Diffraction and Theoretical Calculations
Vorontsov, Ivan I.; Graber, Tim; Kovalevsky, Andrey Yu.; Novozhilova, Irina V.; Gembicky, Milan; Chen, Yu-Sheng; Coppens, Philip; (Toledo); (SUNYB); (Ariz)
Time-resolved crystallography and density functional theory calculations are used to analyze the geometric and electronic changes that occur upon photoexcitation of [Cu(I)(dmp)(dppe)]{sup +} in crystalline [Cu(I)(dmp)(dppe)][PF{sub 6}] [dmp = 2,9-dimethyl-1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino)ethane]. In the pump-probe experiment, laser and X-ray pulses are synchronized to capture an image of the instantaneous molecular distortions in the transient triplet state. Parallel theoretical calculations, with the phenyl groups replaced by methyl groups, yield information on the distortion of the isolated cation and the change in electron density upon excitation. The experimental distortions are significantly less than the calculated values and are different for the two independent molecules in the asymmetric unit; these findings are attributed to the constraining influence of the crystal matrix. The calculations indicate that the electron transfer upon excitation is mostly from the dmpe ligand to the dmp ligand, while the Cu atomic charge changes by only {approx}+0.1 e, although the charge distribution on Cu is significantly affected. As found for homoleptic [Cu(I)(dmp){sub 2}]{sup +}, the change in the population of the Cu atom is close to the calculated difference between the corresponding Cu(II) and Cu(I) complexes. Charge density difference maps confirm these conclusions and show a large rearrangement of the electron density on the Cu atom upon excitation.
Theoretical analysis of 630-nm band GaInP-AlGaInP strained quantum-well lasers considering continuum states
Shun Tung Yen; Chien-Ping Lee
GaInP-AlGaInP strained quantum-well lasers with emission wavelength at 630-nm band are theoretically analyzed in detail and then optimized. The valence band structure of quantum wells is obtained by evaluating the 6ū6 Luttinger-Kohn Hamiltonian including the coupling among the heavy hole, the light hole, and the spin-orbital spilt-off hole bands. The effect of optical transition from\\/to continuum states not confined to
A Initio Calculations Performed on Carbon Monoxide Adsorption on the IRON(100) Surface and Complementing Theoretical Techniques
NASA Astrophysics Data System (ADS)
Meehan, Timothy Erickson
Unrestricted Hartree-Fock calculations were performed on Fe_{x}CO clusters to model the CO(alpha_1), CO(alpha_2), and CO( alpha_3) adsorptions on the Fe(100) surface. Clusters of FeCO(C_{4v}) and a multiplicity of 5, Fe_2 CO(C_{2v}) and a multiplicity of 7, and Fe_2CO(C _{s}) and a multiplicity of 7, were constructed to model, respectively, the adsorption for the on top site, bridging site, and tilted CO structure at the 4-fold site. The CO position was optimized with respect to the Fe bulk distances using gradient techniques and the partial geometry optimization. CO stretching frequencies were calculated for each optimized geometry, and we find no evidence supporting CO adsorption in the bridging site. Using a full basis set the calculated CO stretching frequencies for the FeCO(C_{4v}), Fe_2CO(C_ {2v}), and the Fe_2 CO(C_{s}) clusters are 1992, 1767, and 771 cm^{ -1}, respectively. The CSOV analysis was executed to analyze the major orbital interactions between the CO and Fe_{x} clusters. For both Fe_2CO clusters, the CO pi^* perpendicular to the Fe _2 axis had a more significant contribution involving the pi backdonation from the Fe_2 clusters. Furthermore, the spin minority d electrons are mainly responsible for the pi backdonation. Due to problems with SCF convergence incurred during the Fe_{x}CO studies, we were forced to investigate a number of different techniques to achieve SCF convergence. Therefore, techniques that generate starting guesses of the eigenvectors for the SCF procedure and techniques used to accelerate SCF convergence are reviewed. The standard guesses of H _{core} and charge build -up are examined, and we introduce a new incremental cluster method for generating starting guesses for large clusters. The standard techniques of extrapolation, DIIS, damping, level shifting, restrict, and symmetry blocking are examined, and we also developed the hacker method and partial geometry optimization as new techniques to achieve SCF convergence. Results of the review indicate that the most important element for obtaining SCF convergence is the starting guess. A procedure for performing transition metal cluster calculations is outlined.
New Benchmarks from Tokamak Experiments for Theoretical Calculations of the Dielectronic Satellite Spectra of Helium-like Ions
M. Bitter; M.F. Gu; L.A. Vainshtein; P. Beiersdorfer; G. Bertschinger; O. Marchuk; R. Bell; B. LeBlanc; K.W. Hill; D. Johnson; L. Roquemore
Dielectronic satellite spectra of helium-like argon, recorded with a high-resolution X-ray crystal spectrometer at the National Spherical Torus Experiment, were found to be inconsistent with existing predictions resulting in unacceptable values for the power balance and suggesting the unlikely existence of non-Maxwellian electron energy distributions. These problems were resolved with calculations from a new atomic code. It is now possible to perform reliable electron temperature measurements and to eliminate the uncertainties associated with determinations of non-Maxwellian distributions.
A Theoretical Model for Calculating Voltage Sensitivity of Ion Channels andĀthe Application on Kv1.2 Potassium Channel
Yang, Huaiyu; Gao, Zhaobing; Li, Ping; Yu, Kunqian; Yu, Ye; Xu, Tian-Le; Li, Min; Jiang, Hualiang
Voltage sensing confers conversion of a change in membrane potential to signaling activities underlying the physiological processes. For an ion channel, voltage sensitivity is usually experimentally measured by fitting electrophysiological data to Boltzmann distributions. In our study, a two-state model of the ion channel and equilibrium statistical mechanics principle were used to test the hypothesis of empirically calculating the overall voltage sensitivity of an ion channel on the basis of its closed and open conformations, and determine the contribution of individual residues to the voltage sensing. We examined the theoretical paradigm by performing experimental measurements with Kv1.2 channel and a series of mutants. The correlation between the calculated values and the experimental values is at respective level, R2Ā= 0.73. Our report therefore provides inĀsilico prediction of key conformations and has identified additional residues critical for voltage sensing. PMID:22768937
Segmented crystalline scintillators: empirical and theoretical investigation of a high quantum efficiency EPID based on an initial engineering prototype CsI(TI) detector.
Sawant, Amit; Antonuk, Larry E; El-Mohri, Youcef; Zhao, Qihua; Wang, Yi; Li, Yixin; Du, Hong; Perna, Louis
Modern-day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft-tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a 40 mm thick, segmented crystalline CsI(Tl) detector incorporated into an indirect-detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of 160 x 160 optically isolated, crystalline CsI(Tl) elements spaced at 1016 microm pitch. The detector was coupled to an indirect detection-based active matrix array having a pixel pitch of 508 microm, with each detector element registered to 2 x 2 array pixels. The performance of the prototype imager was evaluated under very low-dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast-B phosphor screen. Detailed quantitative measurements were performed in order to determine the x-ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast-detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero-frequency DQE (approximately 22%) compared to that of the conventional AMFPI (approximately 1%). The measured zero-frequency DQE was found to be lower than theoretical upper limits (approximately 27%) calculated from Monte Carlo simulations, which were based solely on the x-ray energy absorbed in the detector-indicating the presence of optical Swank noise. Moreover, due to the nonoptimized nature of this prototype, the spatial resolution was observed to be significantly lower than theoretical expectations. Nevertheless, due to its high quantum efficiency (approximately 55%), the prototype imager exhibited significantly higher DQE than that of the conventional AMFPI across all spatial frequencies. In addition, the frequency-dependent DQE was observed to be relatively invariant with respect to the amount of incident radiation, indicating x-ray quantum limited behavior. Images of the contrast-detail phantom and the head phantom obtained using the prototype system exhibit good visualization of relatively large, low-contrast features, and appear significantly less noisy compared to similar images from a conventional AMFPI. Finally, Monte Carlo-based theoretical calculations indicate that, with proper optimization, further, significant improvements in the DQE performance of such imagers could be achieved. It is strongly anticipated that the realization of optimized versions of such very high-DQE EPIDs would enable megavoltage projection imaging at very low doses, and tomographic imaging from a "beam's eye view" at clinically acceptable doses. PMID:16696482
Calculation of calorific values of coals from ultimate analyses: theoretical basis and geochemical implications. Final report. Part 8
Given, P.H.; Weldon, D.; Zoeller, J.H.
The various formulae for calculating calorific values for coals from ultimate analyses depend essentially on a propositon due to Dulong, that the heat of combustion of an organic compound is nearly equal to the heats of combustion of the elements in it, multiplied by their percentage content in the compound in question. This proposition assumes that the enthalpy of decomposition is negligible compared with the heat of combustion. The various published formulae, such as that due to Mott and Spooner, include empirical adjustments to allow for the fact that the enthalpy of formation or decomposition of no organic compound is zero (except rarely by chance). A new equation is proposed, which excludes empirical correction terms but includes a term explicitly related to the enthalpy of decomposition. As expected from the behavior of known compounds, this enthalpy varies with rank, but it also varies at the same level of rank with the geological history of the sample: rank is not the only source of variance in coal properties. The new equation is at least as effective in predicting calorific values for a set of 992 coals as equivalent equations derived for 6 subsets of the coals. On the whole, the distributions of differences between observed and calculated calorific values are skewed to only a small extent. About 86% of the differences lie between -300 and +300 Btu/lb (+- 700 kJ/kg). 10 references, 7 figures, 4 tables.
Structures and spectroscopic properties of bis(phthalocyaninato) yttrium and lanthanum complexes: theoretical study based on density functional theory calculations.
Zhang, Yuexing; Cai, Xue; Zhou, Yang; Zhang, Xianxi; Xu, Hui; Liu, Zhongqiang; Li, Xiyou; Jiang, Jianzhuang
Density functional theory (DFT) calculations were carried out to describe the molecular structures, molecular orbitals, atomic charges, UV-vis absorption spectra, IR, and Raman spectra of bis(phthalocyaninato) rare earth(III) complexes M(Pc)(2) (M = Y, La) as well as their reduced products [M(Pc)(2)](-) (M = Y, La). Good consistency was found between the calculated results and experimental data. Reduction of the neutral M(Pc)(2) to [M(Pc)(2)]- induces the reorganization of their orbitals and charge distribution and decreases the inter-ring interaction. With the increase of ionic size from Y to La, the inter-ring distance of both the neutral and reduced double-decker complexes M(Pc)(2) and [M(Pc)(2)](-) (M = Y, La) increases, the inter-ring interaction and splitting of the Q bands decrease, and corresponding bands in the IR and Raman spectra show a red shift. The orbital energy level and orbital nature of the frontier orbitals are also described and explained in terms of atomic character. The present work, representing the first systemic DFT study on the bis(phthalocyaninato) yttrium and lanthanum complexes sheds further light on clearly understanding structure and spectroscopic properties of bis(phthalocyaninato) rare earth complexes. PMID:17214477
Nuclear Quantum Effects in Ice Phases and Water from First Principles Calculations
NASA Astrophysics Data System (ADS)
Pamuk, Betul
Despite the simplicity of the molecule, condensed phases of water show many physical anomalies, some of which are still unexplained to date. This thesis focuses on one striking anomaly that has been largely neglected and never explained. When hydrogen (1H) is replaced by deuterium (2 D), zero point fluctuations of the heavy isotope causes ice to expand, whereas in normal isotope effect, heavy isotope causes volume contraction. Furthermore, in a normal isotope effect, the shift in volume should decrease with increasing temperature, while, in ice, the volume shift increases with increasing temperature and persists up to the melting temperature and also exists in liquid water. In this dissertation, nuclear quantum effects on structural and cohesive properties of different ice polymorphs are investigated. We show that the anomalous isotope effect is well described by first principles density functional theory with van der Waals (vdW-DF) functionals within the quasi-harmonic approximation. Our theoretical modeling explains how the competition between the intra- and inter-molecular bonding of ice leads to an anomalous isotope effect in the volume and bulk modulus of ice. In addition, we predict a normal isotope effect when 16O is replaced by 18O, which is experimentally confirmed. Furthermore, the transition from proton disordered hexagonal phase, ice Ih to proton ordered hexagonal phase, ice XI occurs with a temperature difference between 1H and 2D of 6K, in good agreement with experimental value of 4K. We explain, for first time for that this temperature difference is entirely due to the zero point energy. In the second half of this thesis, we expand our study to the other ice phases: ice Ic, ice IX, ice II, ice VIII, clathrate hydrates, and low and high density amorphous ices. We employ the methodology that we have developed to investigate the isotope effect in structures with different configurations. We show that there is a transition from anomalous isotope effect to normal isotope effect in these structures as the density increases. We analyse the bonding mechanism of these structures and make links to the most important anomalies of liquid water.
Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations
NASA Astrophysics Data System (ADS)
Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R.
A combined experimental-theoretical study of optically pumped nuclear magnetic resonance (OPNMR) has been performed in a GaAs /A l0.1G a0.9As quantum well film epoxy bonded to a Si substrate with thermally induced biaxial strain. The photon energy dependence of the Ga OPNMR signal was recorded at magnetic fields of 4.9 and 9.4 T at a temperature of 4.8-5.4 K. The data were compared to the nuclear spin polarization calculated from the electronic structure and differential absorption to spin-up and spin-down states of the electron conduction band using a modified k .p model based on the Pidgeon-Brown model. Comparison of theory with experiment facilitated the assignment of features in the OPNMR energy dependence to specific interband Landau level transitions. The results provide insight into how effects of strain and quantum confinement are manifested in optical nuclear polarization in semiconductors.
Theoretical study of terahertz quantum well photodetectors: Effect of metallic diffraction coating
NASA Astrophysics Data System (ADS)
Hewageegana, Prabath; Apalkov, Vadym
The possibility of enhancement of sensitivity of quantum well photodetectors by adding metallic diffraction coating on top of the dielectric layer of photodetectors is studied. With the grating the spatial distribution of the intensity of electromagnetic wave within the active region of the photodetector is highly non-uniform with the intensity variation over a few orders of magnitude within a period of the grating. This effect is due to the coupling of surface plasmon with incident electromagnetic wave. At terahertz frequencies the average intensity of the transmitted radiation wave through the grating strongly depends on the dielectric constant of metal.
Development of Multiscale Simulator for Dye-Sensitized TiO2 Nanoporous Electrode Based on Quantum Chemical Calculation
NASA Astrophysics Data System (ADS)
Ogiya, Kei; Lv, Chen; Suzuki, Ai; Sahnoun, Riadh; Koyama, Michihisa; Tsuboi, Hideyuki; Hatakeyama, Nozomu; Endou, Akira; Takaba, Hiromitsu; Kubo, Momoji; Del Carpio, Carlos A.; Miyamoto, Akira
In this study, we have developed a novel multiscale simulator for a dye-sensitized TiO2 porous electrode. In the simulator, we can estimate the properties of the dye-sensitized TiO2 porous electrode using the three-dimensional mesoscopic structure model constructed on the basis of our original porous structure simulator. The microscopic physical properties of the materials were estimated by quantum chemistry calculation using a tight-binding quantum chemical molecular dynamics program. From the calculation results, we determined the absorption coefficient and the diffusion coefficient of excited carriers used in the macroscopic simulation for photoelectrode characteristics. By using this multiscale simulator, we will be able to determine the best electrode system efficiently.
Interaction of curcumin with Al(III) and its complex structures based on experiments and theoretical calculations
NASA Astrophysics Data System (ADS)
Jiang, Teng; Wang, Long; Zhang, Sui; Sun, Ping-Chuan; Ding, Chuan-Fan; Chu, Yan-Qiu; Zhou, Ping
Curcumin has been recognized as a potential natural drug to treat the Alzheimer's disease (AD) by chelating baleful metal ions, scavenging radicals and preventing the amyloid ? (A?) peptides from the aggregation. In this paper, Al(III)-curcumin complexes with Al(III) were synthesized and characterized by liquid-state 1H, 13C and 27Al nuclear magnetic resonance (NMR), mass spectroscopy (MS), ultraviolet spectroscopy (UV) and generalized 2D UV-UV correlation spectroscopy. In addition, the density functional theory (DFT)-based UV and chemical shift calculations were also performed to view insight into the structures and properties of curcumin and its complexes. It was revealed that curcumin could interact strongly with Al(III) ion, and form three types of complexes under different molar ratios of [Al(III)]/[curcumin], which would restrain the interaction of Al(III) with the A? peptide, reducing the toxicity effect of Al(III) on the peptide.
On the prediction of thermal stability of nitroaromatic compounds using quantum chemical calculations
Paris-Sud XI, Universitķ de
ranks at top of physicochemical hazards that may be feared from the use of a given chemical [11 On the prediction of thermal stability of nitroaromatic compounds using quantum chemical a new approach to predict thermal stability of nitroaromatic compounds based on quantum chemical
Torsional energy levels of CH?OH?/CH?OD?/CD?OD? studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations.
Dai, Zuyang; Gao, Shuming; Wang, Jia; Mo, Yuxiang
The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling. PMID:25318721
Bridging quantum chemistry and nuclear structure theory: Coupled-cluster calculations for closed- and open-shell nuclei
NASA Astrophysics Data System (ADS)
Piecuch, Piotr; W?och, Marta; Gour, Jeffrey R.; Dean, David J.; Hjorth-Jensen, Morten; Papenbrock, Thomas
We review basic elements of the single-reference coupled-cluster theory and discuss large scale ab initio calculations of ground and excited states of 15O, 16O, and 17O using coupled-cluster methods and algorithms developed in quantum chemistry. By using realistic two-body interactions and the renormalized form of the Hamiltonian obtained with a no-core G-matrix approach, we obtain the converged results for 16O and promising preliminary results for 15O and 17O at the level of two-body interactions. The calculated properties other than energies include matter density, charge radius, and charge form factor. The relatively low costs of coupled-cluster calculations, which are characterized by the low-order polynomial scaling with the system size, enable us to probe large model spaces with up to 7 or 8 major oscillator shells, for which non-truncated shell-model calculations for nuclei with A = 15 17 active particles are presently not possible. We argue that the use of coupled-cluster methods and computer algorithms developed by quantum chemists to calculate properties of nuclei is an important step toward the development of accurate and affordable many-body theories that cross the boundaries of various physical sciences.
Theoretical investigation of some parameters into the behavior of quantum dot solar cells
NASA Astrophysics Data System (ADS)
Nasr, A.; Aly, A.
The main goal of this paper is to determine the accurate values of two parameters namely the surface generationŚrecombination rate and the average total number of electrons density generated in the i-region. These values will enhance the performance of quantum dot solar cells (QDSCs). In order to determine these values, this paper concentrates on the optical generation lifetime, the recombination lifetime, and the effective density state in QDs. Furthermore, these parameters are studied in relation with the average total number of electrons density. The values of the surface generationŚrecombination rate are found to be negative, which implies that the generation process is dominant in the absorption quantum dot region. Consequently, induced photocurrent density relation with device parameters is determined. The results ensure that QDSCs can have higher response photocurrent and then improve the power conversion efficiency. Moreover, the peak value of the average total number of electrons density is achieved at the UV range and is extended to the visible range, which is adequate for space and ground solar applications.
Calculation of the structural dependence of infrared absorption in p-type strained layer SiGe\\/Si quantum wells
Tsyr-Shyang Liou; Tahui Wang; Chun-Yen Chang
A study of infrared absorption due to intersubband transitions in p-type Si1?xGex\\/Si quantum wells has been performed. The influence of the hole envelope wave-function and the subband structure on the absorption characteristics is evaluated. In the calculation, the subbands in a SiGe strained layer are computed by using a bond orbital model, which combines the k?p and the tight-binding methods,
Quantum Mechanics\\/Molecular Mechanics Calculation of the Raman Spectra of the Phycocyanobilin Chromophore in ?-C-Phycocyanin
Maria Andrea Mroginski; Franz Mark; Walter Thiel; Peter Hildebrandt
We have established a quantum mechanics (QM)\\/molecular mechanics (MM) hybrid method for calculating the Raman spectra of protein-bound cofactors using the ?-subunit of C-phycocyanin containing a phycocyanobilin (PCB) chromophore as a test case. The PCB cofactor was described with density functional theory, whereas the protein matrix was treated with the CHARMM force field. The Hessian matrix of the QM region
Characterizing Surface Acidic Sites in Mesoporous-Silica-Supported Tungsten Oxide Catalysts Using Solid State NMR and Quantum Chemistry Calculations
Jian Z. Hu; Ja Hun Kwak; Yong Wang; Mary Y. Hu; Romulus VF Turcu; Charles HF Peden
The acidic sites in dispersed tungsten oxide supported on SBA-15 mesoporous silica were investigated using a combination of pyridine titration, both fast-, and slow-MAS ╣N NMR, static ▓H NMR, and quantum chemistry calculations. It is found that the bridged acidic -OH groups in surface adsorbed tungsten dimers (i.e., W-OH-W) are the Broensted acid sites. The unusually strong acidity of these
Ion-molecule reactions involving HCO+ and N2H+: Isotopologue equilibria from new theoretical calculations and consequences for interstellar isotope fractionation
NASA Astrophysics Data System (ADS)
Mladenovi?, M.; Roueff, E.
Aims: We revisit with new augmented accuracy the theoretical dynamics of basic isotope exchange reactions involved in the 12C/13C, 16O/18O, and 14N/15N balance because these reactions have already been studied experimentally in great detail. Methods: Electronic structure methods were employed to explore potential energy surfaces, full-dimensional rovibrational calculations to compute rovibrational energy levels that are numerically exact, and chemical network models to estimate the abundance ratios under interstellar conditions. Results: New exothermicities, derived for HCO+ reacting with CO, provide rate coefficients markedly different from previous theoretical values in particular at low temperatures, resulting in new abundance ratios relevant for carbon chemistry networks. In concrete terms, we obtain a reduction in the abundance of H12C18O+ and an increase in the abundance of H13C16O+ and D13C16O+. In all studied cases, the reaction of the ion with a neutral polarizable molecule proceeds through the intermediate proton-bound complex found to be very stable. For the complexes OCH+ĘĘĘ CO, OCH+ĘĘĘ OC, COHOC+, N2ĘĘĘ HCO+, N2H+ĘĘĘ OC, and N2HN2+, we also calculated vibrational frequencies and dissociation energies. Conclusions: The linear proton-bound complexes possess sizeable dipole moments, which may facilitate their detection.
Numerical calculation of electronic states in ellipsoidal finite-potential quantum dots with an off-centered impurity
NASA Astrophysics Data System (ADS)
Xue, Changfeng; Deng, Shaozhong
In this article, the computational procedure to calculate wave-functions and energies of spherical quantum dots with finite barriers and a shallow donor impurity located anywhere inside is extended to prolate spheroidal quantum dots. As in the spherical case, the extension of the procedure fully takes into account polarization effects originating from the dielectric mismatch at the dot surface. Particular attentions are paid to the calculations of self-polarization potential energy so as to overcome the mathematical divergence in the self energy when the sharp step-like dielectric interface is assumed between the dot and the surrounding matrix. In this regard, the so-called three-layer dielectric models, including the novel quasi-harmonic dielectric model, are employed. The procedure is implemented to calculate energy states of a prolate spheroidal quantum dot with a hydrogenic donor impurity located at the polar axis of the dot, held at a finite confining potential. The resulting code is then employed to carry out an illustrative study on the effects of the dielectric mismatch, the impurity location, and the choice of dielectric models to the electronic energy in the dot.
Molecular structure, spectroscopic characterization of (S)-2-Oxopyrrolidin-1-yl Butanamide and ab initio, DFT based quantum chemical calculations
NASA Astrophysics Data System (ADS)
Ramya, T.; Gunasekaran, S.; Ramkumaar, G. R.
The experimental and theoretical spectra of (S)-2-Oxopyrrolidin-1-yl Butanamide (S2OPB) were studied. FT-IR and FT-Raman spectra of S2OPB in the solid phase were recorded and analyzed in the range 4000-450 and 5000-50 cm-1 respectively. The structural and spectroscopic analyses of S2OPB were calculated using ab initio Hartree Fock (HF) and density functional theory calculations (B3PW91, B3LYP) with 6-31G(d,p) basis set. A complete vibrational interpretation has been made on the basis of the calculated Potential Energy Distribution (PED). The HF, B3LYP and B3PW91 methods based NMR calculation has been used to assign the 1H NMR and 13C NMR chemical shift of S2OPB. Comparative study on UV-Vis spectral analysis between the experimental and theoretical (B3PW91, B3LYP) methods and the global chemical parameters and local descriptor of reactivity through the Fukui function were performed. Finally the thermodynamic properties of S2OPB were calculated at different temperatures and the corresponding relations between the properties and temperature were also studied.
Synthesis, molecular structure, theoretical calculation, DNA/protein interaction and cytotoxic activity of manganese(III) complex with 8-hydroxyquinoline.
Thamilarasan, V; Sengottuvelan, N; Sudha, A; Srinivasan, P; Siva, A
Manganese(III) complex (1) [Mn(8-hq)3] (where 8-hq=8-hydroxyquinoline) has been synthesized and characterized by elemental, spectral (UV-vis, FT-IR) and thermal analysis. The structure of complex (1) has been determined by single crystal X-ray diffraction studies and the configuration around manganese(III) ion was elongated octahedral coordination geometry. Density functional theory calculations were performed for ligand and its complex. Binding studies of ligand and complex 1 with calf thymus DNA (CT-DNA) was investigated by absorption, fluorescence, circular dichroic (CD) spectroscopy and viscosity measurements. Absorption spectral studies revealed that ligand and complex 1 binds to DNA groove and its intrinsic binding strength has been found to be 2.57ū10(4) and 2.91ū10(4)M(-1). A molecular docking study confirm that the complex 1 is a minor groove binder and was stabilized through hydrogen bonding interactions. Complex 1 exhibits a good binding propensity to bovine serum albumin (BSA) protein. The in vitro cytotoxicity study of complex 1 on breast cancer cell line (MCF-7) indicate that it has the potential to act as effective anticancer drug, with IC50 values of 3.25?M. The ligand and its complex have been screened for antimicrobial activities and the complex showed better antimicrobial activity than the free ligand. PMID:25550122
Theoretical Calculations and Simulations of Interaction of X-Rays with High-Z Nanomoities for Use in Cancer Radiotherapy
NASA Astrophysics Data System (ADS)
Lim, Sara N.; Pradhan, Anil K.; Nahar, Sultana N.
When used with X-ray radiotherapy, heavy elements (high atomic number Z or HZ) such as gold(Au) and platinum(Pt) have the potential to greatly sensitize and enhance the damage to tumor tissues. While HZ radiosensitization has been shown to be higly effective in reducing tumor sizes, much work still needs to be done to determine the ideal X-ray energy/energy spectrum. The likelihood of photoelectric absorption of X-rays that result in the production of cell-killing Auger electrons relative to the photon scatter in an HZ sensitized tumor has to be determined for treatments using X-rays from various sources and energies to assess their efficacy. In this report, we present computations that outline the dependence of photoelectric absorption on X-ray energy. The relative X-ray absorption by a radiosensitized tumor was calculated to contrast the efficacy of different X-ray sources in Auger electron production at different tumor depths. Enhanced photoabsorption of low-energy X-rays from broadband sources in the keV range is shown to be much higher than from those in the MeV range. In addition, with the use of the Monte Carlo code package Geant4, we present the total X-ray energy deposited into a radiosensitized tumor located at different depths in a phantom. The enhancement in radiation dose deposition will also be analysed at the microscopic cellular level to determine the HZ radiosensitizer concentration required. Potential use of monochromatic X-rays for more precise HZ radiosensitization will also be described.
Computer-Oriented Treatment of High Symmetry in Quantum-Chemical Calculations of Correlated Electronic States
NASA Astrophysics Data System (ADS)
Kuprievich, V. A.; Kapitanchuk, O. L.; Shramko, O. V.
Recent achievements in the synthesis of novel substances and materials raise specific problems in computational quantum chemistry demanding to consider electronic structure multiatomic molecular systems in excited and ionic states beyond one-electron approaches. The proposed computational treatment of problem of electron correlation with emphasis on the symmetry-induced degeneracy of molecular states is discussed. It is essentially based on the theory of symmetry molecular invariants that supposes (i) use of fixed reference symmetry base and (ii) determination of invariant expansions for two-electron integrals and energies. The method successively takes full advantage of the relations between the integrals defined on symmetry molecular orbitals (MO). Using the symmetry-similarity principle within the model with two-center electron - electron interaction a simple computational technique is elaborated enabling to represent each integral from complete set as an expansion of a few independent integrals [1,2]. The technique is specified for the most complicated case of icosahedral (Ih) symmetry which is inherent to fullerene C60. It is considered for (i) the configurations (t1u + t1g), the symmetries of two lowest vacant MOs and (ii) for upper occupied hu-shell. The reference symmetry basis sets (mostly with integer components) are presented enabling to obtain the most results in a mathematically rigorous form thus avoiding round-off errors. Energy functionals constructed for all multiplet states of multi-charged ions are reduced to simple form involving only five (h-shell) or six ((t1u + t1g) case) independent integrals (instead of 120 or 231, respectively, in the general case) thus enabling to reduce full-CI or multiconfigurational self-consistent-field calculations of multicharged ions within the corresponding orbital spaces. Applications of the proposed approach are presented to the C60 anion states, which are the case in superconducting fullerides K3C60 and Rb3C60. Some effects of electron interactions within quasi-pi-electron model with different interelectron potentials are considered [3].
Analysis of the two-photon absorption spectrum of benzonitrile based on the direct quantum-mechanical calculation of the intensity distribution
NASA Astrophysics Data System (ADS)
Burova, T. G.; Anashkin, A. A.
A direct quantum-mechanical calculation of the intensity distribution in the two-photon absorption spectrum of benzonitrile is performed taking into account the Herzberg-Teller effect. The excitation mechanism of all the observed lines, including lines corresponding to the excitation of single-quantum nontotally symmetric vibrations and their combinations with totally symmetric modes, is analyzed. The results of the calculation, performed taking into account the frequency effect and the Duschinsky effect, agree satisfactorily with experimental data. This indicates that it is worthwhile to apply the quantum-mechanical method in calculations of the intensity distribution in the two-photon absorption spectra of cyclic molecules.
Mechanism of Selective Oxidation of Propene to Acrolein on Bismuth Molybdates from Quantum Mechanical Calculations
Goddard III, William A.
Mechanism of Selective Oxidation of Propene to Acrolein on Bismuth Molybdates from Quantum for understanding the fundamental chemical mechanisms underlying the selective oxidation of propene to acrolein to form acrolein, and acrolein desorption. The formation of -allyl intermediate is reversible
Analytic calculation of Witten index in D=2 supersymmetric Yang-Mills quantum mechanics
Piotr Korcyl
We propose a method for the evaluation of Witten index in D=2 supersymmetric Yang-Mills quantum mechanics. We rederive a known result for the SU(2) gauge group and generalize it to any SU(N) gauge group.
Analytical and numerical calculations of spectral and optical characteristics of spheroidal quantum dots
Gusev, A. A., E-mail: email@example.com; Hai, L. L.; Vinitsky, S. I.; Chuluunbaatar, O. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Derbov, V. L.; Klombotskaya, A. S. [Saratov State University (Russian Federation)] [Saratov State University (Russian Federation); Dvoyan, K. G.; Sarkisyan, H. A. [Russian-Armenian (Slavonic) University (Armenia)] [Russian-Armenian (Slavonic) University (Armenia)
In the effective mass approximation for electronic (hole) states of a spheroidal quantum dot with and without external fields the perturbation theory schemes are constructed in the framework of the Kantorovich and adiabatic methods. The eigenvalues and eigenfunctions of the problem, obtained in both analytical and numerical forms, were applied for the analysis of spectral and optical characteristics of spheroidal quantum dots in homogeneous electric fields.
IR and Py-GC/MS spectral simulation of polymer film by quantum chemical and quantum molecular dynamics calculations using the polymer models
NASA Astrophysics Data System (ADS)
Endo, Kazunaka; Hayashi, Koichiro; Ida, Tomonori; Takemura, Tetsuo
We have simulated IR and pyrolysis gas chromatography mass spectrometry (Py-GCMS) spectra of six polymers (PE, PP, PS, PET, N6, PVDF) with the density-functional theory and quantum molecular dynamics calculations on model oligomers. In the former calculations, experimental harmonic frequencies of the polymers have been assigned from the simulated IR spectra. In the latter QMD calculations on thermal decomposition of polymer models, the approximated mass spectra of six (PE, PP, PS, PET, N6, PVDF) polymers were almost in good accordance with the experimental results in Py-GC/MS, although we adjusted the decomposition temperatures to 2240, 2520, and 2800 K as the average absolute deviation of 8%.
Quantum confined Stark effect in Gaussian quantum wells: A tight-binding study
RamĒrez-Morales, A.; MartĒnez-Orozco, J. C.; RodrĒguez-Vargas, I. [Unidad Acadķmica de FĒsica, Universidad Aut¾noma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac. (Mexico)
The main characteristics of the quantum confined Stark effect (QCSE) are studied theoretically in quantum wells of Gaussian profile. The semi-empirical tight-binding model and the Green function formalism are applied in the numerical calculations. A comparison of the QCSE in quantum wells with different kinds of confining potential is presented.
Measuring the absolute disintegration rate of a radioactive gas with a moveable endplate discharge counter (MEP) and theoretical calculation of wall effect
Jaffey, A.H.; Gray, J.; Bentley, W.C.; Lerner, J.L.
A precision built moveable endplate Geiger-Mueller counter was used to measure the absolute disintegration rate of a beta-emitting radioactive gas. A Geiger-Mueller counter used for measuring gaseous radioactivity has <100% counting efficiency owing to two factors: (1) ''end effect,'' due to decreased and distorted fields at the ends where wire-insulator joints are placed, and (2) ''wall effect,'' due to non-ionization by beta particles emitted near to and heading into the wall. The end effect was evaluated by making one end of the counter movable and measuring counting rates at a number of endplate positions. Much of the wall effect was calculated theoretically, based on known data for primary ionization of electrons as a function of energy and gas composition. Corrections were then made for the ''shakeoff'' effect in beta decay and for backscattering of electrons from the counter wall. Measurements and calculations were made for a sample of /sup 85/Kr (beta energy, 0.67 MeV). The wall effect calculation is readily extendable to other beta energies.
Theoretical formalism and experimental verification of line shapes of NMR intermolecular multiple-quantum coherence spectra.
Zheng, Bingwen; Chen, Zhong; Cai, Shuhui; Zhong, Jianhui; Ye, Chaohui
Although the theories and potential applications of intermolecular multiple-quantum coherences (iMQCs) have been under active investigations for over a decade, discussion of iMQC NMR signal formation was mainly confined in the time domain. In this paper, a full line-shape theory was developed to describe iMQC signals in the frequency domain. Relevant features of the line shape, such as peak height, linewidth, and phase, were investigated in detail. Predictions based on the theory agree well with experimental and simulated results. Since radiation-damping effects always couple with iMQCs in highly polarized liquid-state NMR systems, and strongly radiation-damped signals have many spectral characteristics similar to those of iMQCs, a detailed comparison was also made between them from different spectral aspects. With detailed comparison of peak height, linewidth, and phase, this work demonstrates that the iMQC and radiation-damping phenomena result from two completely different physical mechanisms despite that both present similar signal features and coexist in highly polarized liquid-state NMR systems. PMID:16229580
Quantum-mechanical calculation of the intensity distribution in resonance Raman spectra of guanine-cytosine pair
NASA Astrophysics Data System (ADS)
Burova, T. G.; Ten, G. N.; Anashkin, A. A.
The method of quantum-mechanical calculation of the relative line intensities in the resonance Raman (RR) spectra of polyatomic molecules, which was previously applied to the analysis of the spectra of individual cyclic molecules and makes it possible to take into account the Herzberg-Teller and Duschinsky effects, as well as the frequency effect, is applied for the first time to the calculation of the spectra of a pair guanine-cytosine. Satisfactory agreement between the calculated results and the available experimental data is obtained. The particular features of the intensity distribution in the RR spectra of the guanine-cytosine pair excited by laser radiation at 266, 240, 218, and 200 nm are analyzed. The RR spectra of the guanine-cytosine pair are compared with the spectra of the individual guanine and cytosine molecules excited by the laser radiation at the same wavelengths.
Hole subband structure and mobility calculations of double p-type d-doped GaAs quantum wells
NASA Astrophysics Data System (ADS)
Rodriguez-Vargas, I.; Gaggero-Sager, L. M.
We calculate the hole subband structure and the mobility of p-type double -doped (DDD) GaAs quantum wells. The study is performed within the lines of the Thomas-Fermi-Dirac (TFD) approximation, varying the interlayer distance between wells (l) and the impurity density (p2D). We also have analysed the many-body effects. For the mobility calculations we propose a phenomenological formulae, which takes into account the most important scattering mechanism at low temperature (ionised impurities). The study shows that many-body effects are important in the level structure calculations. We have found a maximum mobility at 200 ┼ for an impurity density of 3.0 ū 1012 cm-2.
Calculations of time-dependent observables in non-Hermitian quantum mechanics: The problem and a possible solution
Ido Gilary; Avner Fleischer; Nimrod Moiseyev
The solutions of the time independent Schrodinger equation for non-Hermitian (NH) Hamiltonians have been extensively studied and calculated in many different fields of physics by using L^2 methods that originally have been developed for the calculations of bound states. The existing non-Hermitian formalism breaks down when dealing with wavepackets(WP). An open question is how time dependent expectation values can be calculated when the Hamiltonian is NH ? Using the F-product formalism, which was recently proposed, [J. Phys. Chem., 107, 7181 (2003)] we calculate the time dependent expectation values of different observable quantities for a simple well known study test case model Hamiltonian. We carry out a comparison between these results with those obtained from conventional(i.e., Hermitian) quantum mechanics (QM) calculations. The remarkable agreement between these results emphasizes the fact that in the NH-QM, unlike standard QM, there is no need to split the entire space into two regions; i.e., the interaction region and its surrounding. Our results open a door for a type of WP propagation calculations within the NH-QM formalism that until now were impossible.
Quantum mechanical calculation of the collision-induced absorption spectra of N2-N2 with anisotropic interactions.
Karman, Tijs; Miliordos, Evangelos; Hunt, Katharine L C; Groenenboom, Gerrit C; van der Avoird, Ad
We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling. PMID:25725730
Theoretical Prediction of Hydrogen-Bond Basicity pKBHX Using Quantum Chemical Topology Descriptors
Hydrogen bonding plays an important role in the interaction of biological molecules and their local environment. Hydrogen-bond strengths have been described in terms of basicities by several different scales. The pKBHX scale has been developed with the interests of medicinal chemists in mind. The scale uses equilibrium constants of acidĘĘĘbase complexes to describe basicity and is therefore linked to Gibbs free energy. Site specific data for polyfunctional bases are also available. The pKBHX scale applies to all hydrogen-bond donors (HBDs) where the HBD functional group is either OH, NH, or NH+. It has been found that pKBHX can be described in terms of a descriptor defined by quantum chemical topology, ?E(H), which is the change in atomic energy of the hydrogen atom upon complexation. Essentially the computed energy of the HBD hydrogen atom correlates with a set of 41 HBAs for five common HBDs, water (r2 = 0.96), methanol (r2 = 0.95), 4-fluorophenol (r2 = 0.91), serine (r2 = 0.93), and methylamine (r2 = 0.97). The connection between experiment and computation was strengthened with the finding that there is no relationship between ?E(H) and pKBHX when hydrogen fluoride was used as the HBD. Using the methanol model, pKBHX predictions were made for an external set of bases yielding r2 = 0.90. Furthermore, the basicities of polyfunctional bases correlate with ?E(H), giving r2 = 0.93. This model is promising for the future of computation in fragment-based drug design. Not only has a model been established that links computation to experiment, but the model may also be extrapolated to predict external experimental pKBHX values. PMID:24460383
Phosphoryl transfers of the phospholipase D superfamily: a quantum mechanical theoretical study.
DeYonker, Nathan J; Webster, Charles Edwin
The HKD-containing Phospholipase D superfamily catalyzes the cleavage of the headgroup of phosphatidylcholine to produce phosphatidic acid and choline. The mechanism of this cleavage process is studied theoretically. The geometric basis of our models is the X-ray crystal structure of the five-coordinate phosphohistidine intermediate from Streptomyces sp . Strain PMF (PDB Code = 1V0Y ). Hybrid ONIOM QM:QM methodology with Density Functional Theory (DFT) and semiempirical PM6 (DFT:PM6) is used to acquire thermodynamic and kinetic data for the initial phosphoryl transfer, subsequent hydrolysis, and finally, the formation of the experimentally observed ?dead-end? phosphohistidine product (PDB Code = 1V0W ). The model contains nineteen amino acid residues (including the two highly conserved HKD-motifs), four explicit water molecules, and the substrate. Via computations, the persistence of the short-lived five-coordinate phosphorane intermediate on the minutes times scale is rationalized. This five-coordinate phosphohistidine intermediate energetically exists between the hydrolysis event and ?substrate reorganization? (the reorganization of the in vitro model substrate within the active site). Computations directly support the thermodynamic favorability of the in vitro four-coordinate phosphohistidine product. In vivo, the activation energy of substrate reorganization is too high, perhaps due to a combination of substrate immobility when embedded in the lipid bilayer, as well as its larger steric bulk compared to the compound used in the in vitro substrate soaks. On this longer time scale, the enzyme will migrate along the lipid membrane toward its next substrate target, rather than promote the formation of the dead-end product. PMID:24007383
A theoretical model for electron transfer in ion-atom collisions: Calculations for the collision of a proton with an argon atom
NASA Astrophysics Data System (ADS)
Wang, F.; Xu, X. C.; Hong, X. H.; Wang, J.; Gou, B. C.
We have developed a theoretical model of ion-atom collisions based on the time-dependent density-functional theory. We solve the time-dependent Kohn-Sham equation for electrons employing the real-space and real-time method, while the ion dynamics are described in classical mechanics by the Ehrenfest method. Taking advantage of the real-space grid method, we introduce the ōcoordinate space translationö technique to allow one to focus on a certain space of interest. Benchmark calculations are given for collisions between proton and argon over a wide range of impact energy. Electron transfer total cross sections showed a fairly good agreement with available experimental data.
In-vitro measurement of two-dimensional temperature distribution during laser-induced interstitial thermotherapy (LITT) and comparison with theoretical calculations
NASA Astrophysics Data System (ADS)
Roggan, Andre; Mesecke von Rheinbaben, Ingolf; Schruender, Stephan; Mueller, Gerhard J.
Laser-induced thermotherapy is a method to treat pathologic sites of inner organs and oblique tissues with laser radiation. The radiation is transmitted via optical fibers and applied using specially designed laser applicators which are mounted to the distal fiber end. Different types of applicators have been developed recently for an effective treatment of large lesions in short periods of time. Two experimental set-ups are presented to measure the optical and thermal applicator patterns at various wavelengths and tissues. One set-up applies the integrating sphere technique to characterize the axial radiation distribution of LITT-applicators. The second set-up was developed to measure two-dimensional temperature distributions in-vitro during a laser application. It consists of a tissue phantom which could be opened like a book and enabled the uptake of thermocamera measurements. The applicator of interest was fixed between both slabs of the phantom. Measurements were carried out with various types of applicators (bare-fiber, diffusing tip, ring-mode, scattering-dome, internally cooled applicator) with a Nd:YAG laser (1064 nm) and a diode laser (980 nm). The results showed that the applicator designs yielded various maximum temperatures between 90 degrees Celsius and 260 degrees Celsius. The measurements for an internally cooled applicator were compared with theoretical calculations of photon- and heat diffusion in scattering media, applying Monte- Carlo simulations and finite difference methods. The measurements corresponded well with the theoretical simulations.
A critical evaluation of the s-cis-trans isomerism of 2-acetylpyrrole and its N-methyl derivative through infrared and NMR spectroscopies and theoretical calculations
NASA Astrophysics Data System (ADS)
Ducati, Lucas C.; Braga, Carolyne B.; Rittner, Roberto; Tormena, Clßudio F.
Literature data are controversial regarding the conformational equilibria of 2-acetylpyrrole (AP) and its N-methyl derivative (AMP). Now, a detailed study through infrared spectroscopy and theoretical calculations has shown that previous data were erroneously interpreted, since only a N,O-cis conformer is present in solution and that it is the stable conformer in the isolated state (?Etrans-cis = 5.05 kcal mol-1, for AP; ?Etrans-cis = 7.14 kcal mol-1, for AMP). Carbonyl and Nsbnd H absorption data in different solvents, supported by theoretical results taking into account the solvent effects [at IEFPCM-B3LYP/6-311++G(3df,3p) level of theory] clearly demonstrated that only the N,O-cis conformer is present in solution. However, a doublet was observed for AP, in CCl4, which can be attributed to this conformer and the lowest wavenumber component to the cis dimer form, stabilized through intermolecular hydrogen bonds (NH⋯Odbnd C). The overall preference for the N,O-cis conformer, in AP and AMP, as interpreted by the NBO analysis, indicated that the hyperconjugative effect is the main contribution to stabilize this rotamer, overcoming the possible steric repulsion. 13C NMR experiments at low temperature in two different solvents (CS2/CDCl2 and acetone-d6) confirmed the occurrence of a single conformer since no separated signals were observed.
QUANTUM MECHANICAL CALCULATIONS OF CHARGE EFFECTS ON GATING THE KcsA CHANNEL
Kariev, Alisher M.; Znamenskiy, Vasiliy S.; Green, Michael E.
A series of ab initio (density functional) calculations were carried out on side chains of a set of amino acids, plus water, from the (intracellular) gating region of the KcsA K+ channel. Their atomic coordinates, except hydrogen, are known from X-ray structures[1¢3], as are the coordinates of some water oxygen atoms. The 1k4c structure is used for the starting coordinates. Quantum mechanical optimization, in spite of the starting configuration, places the atoms in positions much closer to the 1j95, more tightly closed, configuration. This state shows four water molecules forming a ōbasketö under the Q119 side chains, blocking the channel. When a hydrated K+ approaches this ōbasketö, the optimized system shows a strong set of hydrogen bonds with the K+ at defined positions, preventing further approach of the K+ to the basket. This optimized structure with hydrated K+ added shows an ice-like 12 molecule nanocrystal of water. If the water molecules exchange, unless they do it as a group, the channel will remain blocked. The ōbasketö itself appears to be very stable, although it is possible that the K+ with its hydrating water molecules may be more mobile, capable of withdrawing from the gate. It is also not surprising that water essentially freezes, or forms a kind of glue, in a nanometer space; this agrees with experimental results on a rather different, but similarly sized (nm dimensions) system[4] It also agrees qualitatively with simulations on channels[5, 6] and on featureless channel-like systems[7], in that it forms a boundary on water that is not obvious from the liquid state. The idea that a atructure is stable, even if individual molecules exchange, is well known, for example from the hydration shell of ions. We show that when charges are added in the form of protons to the domains (one proton per domain), the optimized structure is open. No stable water hydrogen bonds hold it together; an opening of 11.0 ┼ appears, measured diagonally between non-neighboring domains as glutamine 119 carbonyl O ¢ O distance. This is comparable to the opening in the MthK potassium channel structure that is generally agreed to be open. The appearance of the opening is in rather good agreement with that found by Perozo and coworkers. In contrast, in the uncharged structure this diagonal distance is 6.5┼, and the water ōbasketö constricts the uncharged opening still further, with the ice-like structure that couples the K+ ion to the gating region freezing the entrance to the channel. Comparison with our earlier model for voltage gated channels suggests that a similar mechanism may apply in those channels. PMID:17336921
Quantum chemical calculations predict biological function: The case of T cell receptor interaction with a peptide/MHC class I
NASA Astrophysics Data System (ADS)
Antipas, Georgios S. E.; Germenis, Anastasios
A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptideÆs electron spin density and intrinsically expressed by the protonation state of the peptideÆs N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction.
Quantum chemical calculations predict biological function: the case of T cell receptor interaction with a peptide/MHC class I
Antipas, Georgios S. E.; Germenis, Anastasios E.
A combination of atomic correlation statistics and quantum chemical calculations are shown to predict biological function. In the present study, various antigenic peptide-Major Histocompatibility Complex (pMHC) ligands with near-identical stereochemistries, in complexation with the same T cell receptor (TCR), were found to consistently induce distinctly different quantum chemical behavior, directly dependent on the peptide's electron spin density and intrinsically expressed by the protonation state of the peptide's N-terminus. Furthermore, the cumulative coordination difference of any variant in respect to the native peptide was found to accurately reflect peptide biological function and immerges as the physical observable which is directly related to the immunological end-effect of pMHC-TCR interaction. PMID:25713797
Yang Benhui; Stancil, P. C. [Department of Physics and Astronomy and the Center for Simulational Physics, The University of Georgia, Athens, GA 30602 (United States); Balakrishnan, N. [Department of Chemistry, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Forrey, R. C. [Department of Physics, Penn State University, Berks Campus, Reading, PA 19610 (United States); Bowman, J. M. [Department of Chemistry, Emory University, Atlanta, GA 30322 (United States)
New quantum scattering calculations for rotational deexcitation transitions of CO induced by H collisions using two CO-H potential energy surfaces (PESs) from Shepler et al. are reported. State-to-state rate coefficients are computed for temperatures ranging from 1 to 3000 K for CO(v = 0, j) deexcitation from j = 1 to 5 to all lower j' levels, with j being the rotational quantum number. Different resonance structures in the cross sections are attributed to the differences in the anisotropy and the long-range van der Waals well depths of the two PESs. These differences affect rate coefficients at low temperatures and give an indication of the uncertainty of the results. Significant discrepancies are found between the current rate coefficients and previous results computed using earlier potentials, while the current results satisfy expected propensity rules. Astrophysical applications to modeling far infrared and submillimeter observations are briefly discussed.
Quantum mechanical calculations on the potential energy surface for the formation of xenon dichloride and the nature of the (n5-cyclopentadienyl) dicarbonyliron-arene bondĀ
Richardson, Nancy Arline
QUANTUM MECHANICAL CALCULATIONS ON THE POTENTIAL ENERGY SURFACE FOR THE FORMATION OF XENON DICHLORIDE AND THE NATURE OF THE (tis- CYCLOPENTADIENYL) DICARBONYLIRON-ARENE BOND A Thesis by NANCY ARLINE RI~SON Submitted to the Office of Graduate... Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 1993 Major Subject: Chemistry QUANTUM MECHANICAL CALCULATIONS ON THE POTENTIAL ENERGY SURFACE FOR THE FORMATION OF XENON...
PREFACE: Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008) Proceedings of the First International Workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) (Nagoya, Japan, 2-4 July 2008)
NASA Astrophysics Data System (ADS)
Tanaka, Isao; Mizoguchi, Teruyasu; Yamamoto, Tomoyuki
Both electron energy loss near edge structure (ELNES) spectroscopy and x-ray absorption near edge structure (XANES) spectroscopy provide information on the local structural and chemical environments of selected elements of interest. Recent technological progress in scanning transmission electron microscopy has enabled ELNES measurements with atomic column spatial resolution. Very dilute concentrations (nanograms per milliliter or ppb level) of dopants can be observed using third-generation synchrotron facilities when x-ray fluorescence is measured with highly efficient detectors. With such technical developments, ELNES and XANES have become established as essential tools in a large number of fields of natural science, including condensed matter physics, chemistry, mineralogy and materials science. In addition to these developments in experimental methodology, notable progress in reproducing spectra using theoretical methods has recently been made. Using first-principles methods, one can analyze and interpret spectra without reference to experiment. This is quite important since we are often interested in the analysis of exotic materials or specific atoms located at lattice discontinuities such as surfaces and interfaces, where appropriate experimental data are difficult to obtain. Using the structures predicted by reliable first-principles calculations, one can calculate theoretical ELNES and XANES spectra without too much difficulty even in such cases. Despite the fact that ELNES and XANES probe the same phenomenonŚessentially the electric dipole transition from a core orbital to an unoccupied bandŚthere have not been many opportunities for researchers in the two areas to meet and discuss. Theoretical calculations of ELNES spectra have been mainly confined to the electron microscopy community. On the other hand, the theory of XANES has been developed principally by researchers in the x-ray community. Publications describing the methods have been written more-or-less independently by the two communities. The three-day workshop on the Theoretical Calculation of ELNES and XANES (TEX2008) was planned to help remedy this situation. It aimed to demonstrate capability of state-of-the-art theoretical techniques to explain and predict ELNES and XANES spectra, and to allow deep discussion between scientists in the two communities. It also provided an excellent opportunity to introduce experimentalists to the computational techniques available. Invited talks and poster presentations by leading scientists were given on the first day, which was followed by tutorial sessions for five computer programs on the second and third days. Excellent lectures were given by Peter Blaha (Vienna, Austria) on the WIEN2k code, Chris J Pickard (St Andrews, UK) on the CASTEP code, John J Rehr (Seattle, USA) on the FEFF8 code, Frank de Groot (Utrecht, The Netherlands) on the CTM4XAS code, and Hidekazu Ikeno (Kyoto, Japan) on the first-principles CI-multiplet code. Thanks to the enthusiastic participation of more than 100 scientists from around the world, the workshop was a complete success. The aim of this special issue in Journal of Physics: Condensed Matter is to share with the readers the most up-to-date knowledge presented at the workshop. We believe this will prove useful as a reference for researchers in many different fields, as well as an overview of the current status and future directions of theoretical calculations for ELNES and XANES. TEX2008 was a satellite meeting of the First International Symposium on Advanced Microscopy and Theoretical Calculations (AMTC1) (Nagoya, Japan, 29-30 June 2008), which was held in commemoration of the establishment of the Nanostuctures Research Laboratory (NSRL) at the Japan Fine Ceramics Center (JFCC) and as a daughter event of EXPO 2005, Aichi, Japan. A Grant-in-Aid for Scientific Research on Priority Areas 'Nano Materials Science for Atomic-Scale Modification' from the Ministry of Education, Culture, Sports and Technology (MEXT) and support from the Chubu Economic Federation for the workshop are grate
Theoretical and Experimental Studies of the 2 - Grating Coupled Structures for Iii-V Quantum Well Infrared Photodetectors
Yeong-Cheng Wang
This research mainly deals with the quantum efficiency enhancement of QWIPs (Quantum Well Infrared Photodetectors) by using the 2-dimensional (2-D) planar metal grating couplers. The motivation is originated from the intersubband selection rule of quantum well, which requires the polarization of incident infrared (IR) radiation to have a component perpendicular to the quantum well layers. The unique features of the
Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo calculations
AlfĶ, Dario
Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo-volume equation of state, the cohesive energy, and the enthalpy of formation from magnesium bulk and hydrogen gas, performed on periodically repeated systems of up to 1050 atoms, show that all these errors together can
New Regularization-Renormalization Method in Quantum Electrodynamics and Qualitative Calculation on Lamb Shift
Guang-jiong Ni; Haibin Wang
A simple but effective method for regularization-renormalization (R-R) is proposed for handling the Feynman diagram integral (FDI) at one loop level in quantum electrodynamics (QED). The divergence is substituted by some constants to be fixed via experiments. So no counter term, no bare parameter and no arbitrary running mass scale is involved. Then the Lamb Shift in Hydrogen atom can
Bound and quasibound state calculations for biased\\/unbiased semiconductor quantum heterostructures
Emmanuel Anemogiannis; Elias N. Glytsis; Thomas K. Gaylord
A complex transcendental equation valid for a wide range of electron energies for semiconductor quantum heterostructures under unbiased or biased conditions is derived. Its complex roots have as real parts the structure eigenenergy levels, and their imaginary parts are directly related to the lifetime of the corresponding eigenenergies. A numerical method is presented that is capable of extracting all these
Heteroleptic diimine copper (I) complexes with large extinction coefficients: synthesis, quantum chemistry calculations and physico-
Paris-Sud XI, Universitķ de
1 Heteroleptic diimine copper (I) complexes with large extinction coefficients: synthesis, quantum. . Abstract Using the HETPHEN approach, five new heteroleptic copper(I) complexes composed of a push-pull 4 complexes experimentally demonstrate that large light harvesting properties with bis-diimine copper
The theoretical calculation of the Rossby number and the `non-local' convective overturn time for pre-main sequence and early post-main sequence stars
Yong -Cheol Kim; Pierre Demarque
This paper provides estimates of convective turnover time scales for Sun-like stars in the pre-main sequence and early post-main sequence phases of evolution, based on up-to-date physical input for the stellar models. In this first study, all models have solar abundances, which is typical of the stars in the Galactic disk where most of the available data have been collected. A new feature of these models is the inclusion of rotation in the evolutionary sequences, thus making it possible to derive theoretically the Rossby number for each star along its evolutionary track, based on its calculated rotation rate and its local convective turnover time near the base of the convection zone. Global turnover times are also calculated for the complete convection zone. This information should make possible a new class of observational tests of stellar theory which were previously impossible with semi-empirical models, particularly in the study of stellar activity and in research related to angular momentum transfer in stellar interiors during the course of stellar evolution.
Roles of Crystal Surface in Pt-Loaded Titania for Photocatalytic Conversion of Organic Pollutants: A First-Principle Theoretical Calculation.
Chen, Jie-Jie; Wang, Wei-Kang; Li, Wen-Wei; Pei, Dan-Ni; Yu, Han-Qing
Titania modified with nanosized metallic clusters is found to substantially enhance its photocatalytic capacity for renewable energy generation and environmental purification, but the underlying mechanism, especially the roles of crystal surface in noble-metal-loaded TiO2, remain unclear. In this work, such roles in the Pt-loaded anatase TiO2 for the photocatalytic conversion of nitrobenzene (NB), a model pollutant, are explored by first-principle calculations. The theoretical calculations reveal that the Pt-TiO2 complex has a higher catalytic activity toward NB conversion than pure Pt clusters, and the (001) facets of TiO2 in this complex tend to accumulate more positively charged holes and thus have a higher photocatalytic activity than the (101) facets. Furthermore, the thermodynamic and kinetic results also show that the Pt cluster loaded on the (001) surface of anatase TiO2 is favored for NB conversion in the photooxidation pathway. This work deepens our fundamental understanding on the evolution of molecule-photocatalyst interface and provides implications for designing and preparing photocatalysts. PMID:26013255
BAND STRUCTURE CALCULATION FOR QUANTUM DOT SOLAR CELLS USING K.P Som N. Dahal
Honsberg, Christiana
, De 19716 2 Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 1971 material mediated through the confined states in the dot material as schematically shown in Figure 1 the confined states in the dot material as schematically shown in Figure 1. The theoretical efficiency of IBSCs
Charge and Spin States in Schiff Base Metal Complexes with a Disiloxane Unit Exhibiting a Strong Noninnocent Ligand Character: Synthesis, Structure, Spectroelectrochemistry, and Theoretical Calculations.
Cazacu, Maria; Shova, Sergiu; Soroceanu, Alina; Machata, Peter; Bucinsky, Lukas; Breza, Martin; Rapta, Peter; Telser, Joshua; Krzystek, J; Arion, Vladimir B
Mononuclear nickel(II), copper(II), and manganese(III) complexes with a noninnocent tetradentate Schiff base ligand containing a disiloxane unit were prepared in situ by reaction of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with 1,3-bis(3-aminopropyl)tetramethyldisiloxane followed by addition of the appropriate metal(II) salt. The ligand H2L resulting from these reactions is a 2:1 condensation product of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with 1,3-bis(3-aminopropyl)tetramethyldisiloxane. The resulting metal complexes, NiLĘ0.5CH2Cl2, CuLĘ1.5H2O, and MnL(OAc)Ę0.15H2O, were characterized by elemental analysis, spectroscopic methods (IR, UV-vis, X-band EPR, HFEPR, (1)H NMR), ESI mass spectrometry, and single crystal X-ray diffraction. Taking into account the well-known strong stabilizing effects of tert-butyl groups in positions 3 and 5 of the aromatic ring on phenoxyl radicals, we studied the one-electron and two-electron oxidation of the compounds using both experimental (chiefly spectroelectrochemistry) and computational (DFT) techniques. The calculated spin-density distribution and localized orbitals analysis revealed the oxidation locus and the effect of the electrochemical electron transfer on the molecular structure of the complexes, while time-dependent DFT calculations helped to explain the absorption spectra of the electrochemically generated species. Hyperfine coupling constants, g-tensors, and zero-field splitting parameters have been calculated at the DFT level of theory. Finally, the CASSCF approach has been employed to theoretically explore the zero-field splitting of the S = 2 MnL(OAc) complex for comparison purposes with the DFT and experimental HFEPR results. It is found that the D parameter sign strongly depends on the metal coordination geometry. PMID:26030801
Theoretical study and rate constant calculation for the reactions of SH (SD) with Cl2, Br2, and BrCl.
Wang, Li; Liu, Jing-Yao; Li, Ze-Sheng; Sun, Chia-Chung
The mechanisms of the SH (SD) radicals with Cl2 (R1), Br2 (R2), and BrCl (R3) are investigated theoretically, and the rate constants are calculated using a dual-level direct dynamics method. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6-311G(d,p) and MPW1K/6-311G(d,p) levels. Higher-level energies are obtained at the approximate QCISD(T)/6-311++G(3df, 2pd) level using the MP2 geometries as well as by the multicoefficient correlation method based on QCISD (MC-QCISD) using the MPW1K geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of these reactions, which indicate that the reactions may proceed via an indirect mechanism. The enthalpies of formation for the species XSH/XSD (X = Cl and Br) are evaluated using hydrogenation working reactions method. By canonical variational transition-state theory (CVT), the rate constants of SH and SD radicals with Cl2, Br2, and BrCl are calculated over a wide temperature range of 200-2000 K at the a-QCISD(T)/6-311++G(3df, 2pd)//MP2/6-311G(d, p) level. Good agreement between the calculated and experimental rate constants is obtained in the measured temperature range. Our calculations show that for SH (SD) + BrCl reaction bromine abstraction (R3a or R3a') leading to the formation of BrSH (BrSD) + Cl in a barrierless process dominants the reaction with the branching ratios for channels 3a and 3a' of 99% at 298 K, which is quite different from the experimental result of k3a'/k3' = 54 +/- 10%. Negative activation energies are found at the higher level for the SH + Br2 and SH + BrCl (Br-abstraction) reactions; as a result, the rate constants show a slightly negative temperature dependence, which is consistent with the determination in the literature. The kinetic isotope effects for the three reactions are "inverse". The values of kH/kD are 0.88, 0.91, and 0.69 at room temperature, respectively, and they increase as the temperature increases. PMID:15593347
Step-Scan FTIR spectroscopy and quantum chemical calculations of xanthone in the triplet state
NASA Astrophysics Data System (ADS)
Buschhaus, L.; Kleinermanns, K.
Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000-1750 cm-1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.
Exact quantum scattering calculations of transport properties for the H{sub 2}O¢H system
Dagdigian, Paul J., E-mail: firstname.lastname@example.com [Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685 (United States); Alexander, Millard H., E-mail: firstname.lastname@example.com [Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021 (United States)
Transport properties for collisions of water with hydrogen atoms are computed by means of exact quantum scattering calculations. For this purpose, a potential energy surface (PES) was computed for the interaction of rigid H{sub 2}O, frozen at its equilibrium geometry, with a hydrogen atom, using a coupled-cluster method that includes all singles and doubles excitations, as well as perturbative contributions of connected triple excitations. To investigate the importance of the anisotropy of the PES on transport properties, calculations were performed with the full potential and with the spherical average of the PES. We also explored the determination of the spherical average of the PES from radial cuts in six directions parallel and perpendicular to the C{sub 2} axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential.
How Iron-Containing Proteins Control Dioxygen Chemistry: A Detailed Atomic Level Description Via Accurate Quantum Chemical and Mixed Quantum Mechanics/Molecular Mechanics Calculations.
Friesner, Richard A.(Columbia University) [Columbia University; Baik, Mu-Hyun (Columbia University) [Columbia University; Gherman, Benjamin F.(Columbia University) [Columbia University; Guallar, Victor (Washington University) [Washington University; Wirstam, Maria E.(1836) [1836; Murphy, Robert B.(Schrodinger Inc) [Schrodinger Inc; Lippard, Stephen J.(Massachusetts Institute of Technology) [Massachusetts Institute of Technology
Over the past several years, rapid advances in computational hardware, quantum chemical methods, and mixed quantum mechanics/molecular mechanics (QM/MM) techniques have made it possible to model accurately the interaction of ligands with metal-containing proteins at an atomic level of detail. In this paper, we describe the application of our computational methodology, based on density functional (DFT) quantum chemical methods, to two diiron-containing proteins that interact with dioxygen: methane monooxygenase (MMO) and hemerythrin (Hr). Although the active sites are structurally related, the biological function differs substantially. MMO is an enzyme found in methanotrophic bacteria and hydroxylates aliphatic C-H bonds, whereas Hr is a carrier protein for dioxygen used by a number of marine invertebrates. Quantitative descriptions of the structures and energetics of key intermediates and transition states involved in the reaction with dioxygen are provided, allowing their mechanisms to be compared and contrasted in detail. An in-depth understanding of how the chemical identity of the first ligand coordination shell, structural features, electrostatic and van der Waals interactions of more distant shells control ligand binding and reactive chemistry is provided, affording a systematic analysis of how iron-containing proteins process dioxygen. Extensive contact with experiment is made in both systems, and a remarkable degree of accuracy and robustness of the calculations is obtained from both a qualitative and quantitative perspective.
Classical Electrodynamics Coupled to Quantum Mechanics for Calculation of Molecular Optical Properties: a RT-TDDFT/FDTD Approach
Chen, Hanning; McMahon, J. M.; Ratner, Mark A.; Schatz, George C.
A new multiscale computational methodology was developed to effectively incorporate the scattered electric field of a plasmonic nanoparticle into a quantum mechanical (QM) optical property calculation for a nearby dye molecule. For a given location of the dye molecule with respect to the nanoparticle, a frequency-dependent scattering response function was first determined by the classical electrodynamics (ED) finite-difference time-domain (FDTD) approach. Subsequently, the time-dependent scattered electric field at the dye molecule was calculated using the FDTD scattering response function through a multidimensional Fourier transform to reflect the effect of polarization of the nanoparticle on the local field at the molecule. Finally, a real-time time-dependent density function theory (RT-TDDFT) approach was employed to obtain a desired optical property (such as absorption cross section) of the dye molecule in the presence of the nanoparticleÆs scattered electric field. Our hybrid QM/ED methodology was demonstrated by investigating the absorption spectrum of the N3 dye molecule and the Raman spectrum of pyridine, both of which were shown to be significantly enhanced by a 20 nm diameter silver sphere. In contrast to traditional quantum mechanical optical calculations in which the field at the molecule is entirely determined by intensity and polarization direction of the incident light, in this work we show that the light propagation direction as well as polarization and intensity are important to nanoparticle-bound dye molecule response. At no additional computation cost compared to conventional ED and QM calculations, this method provides a reliable way to couple the response of the dye moleculeÆs individual electrons to the collective dielectric response of the nanoparticle.
Quantum chemical calculation of the equilibrium structures of small metal atom clusters
NASA Technical Reports Server (NTRS)
Kahn, L. R.
A decomposition of the molecular energy is presented that is motivated by the atom superposition and electron delocalization physical model of chemical binding. The energy appears in physically transparent form consisting of a classical electrostatic interaction, a zero order two electron exchange interaction, a relaxation energy, and the atomic energies. Detailed formulae are derived in zero and first order of approximation. The formulation extends beyond first order to any chosen level of approximation leading, in principle, to the exact energy. The structure of this energy decomposition lends itself to the fullest utilization of the solutions to the atomic sub problems to simplify the calculation of the molecular energy. If nonlinear relaxation effects remain minor, the molecular energy calculation requires at most the calculation of two center, two electron integrals. This scheme thus affords the prospects of substantially reducing the computational effort required for the calculation of molecular energies.
Quantum Monte Carlo calculations of spectroscopic overlaps in $A \\leq 7$ nuclei
I. Brida; Steven C. Pieper; R. B. Wiringa
We present Green's function Monte Carlo calculations of spectroscopic overlaps for $A \\leq 7$ nuclei. The realistic Argonne v18 two-nucleon and Illinois-7 three-nucleon interactions are used to generate the nuclear states. The overlap matrix elements are extrapolated from mixed estimates between variational Monte Carlo and Green's function Monte Carlo wave functions. The overlap functions are used to obtain spectroscopic factors and asymptotic normalization coefficients, and they can serve as an input for low-energy reaction calculations.
Calculating the Spin-Polarized Image of Electronic Wavefunctions in Quantum Wells
Michael A. Miller; James G. Kempf; Daniel P. Weitekamp
We detail our earlier proposal to image the spin polarization of the wavefunction of excited-state electrons in a quantum well by nuclear magnetic resonance (NMR) with a multiple-pulse line-narrowing sequence synchronized with circularly-polarized light pulses. The modeling explores the effects of competition between optical pumping and thermal relaxation of carrier polarization along with spin-dependent carrier recombination. While the Knight shift
Nonperturbative non-Markovian quantum master equation: Validity and limitation to calculate nonlinear response functions
Akihito Ishizaki; Yoshitaka Tanimura
Based on the influence functional formalism, we have derived a nonperturbative equation of motion for a reduced system coupled to a harmonic bath with colored noise in which the system¢bath coupling operator does not necessarily commute with the system Hamiltonian. The resultant expression coincides with the time-convolutionless quantum master equation derived from the second-order perturbative approximation, which is also equivalent
Calculation of rotational-vibrational preionization in H2 by multichannel quantum defect theory
NASA Astrophysics Data System (ADS)
Jungen, Ch.; Dill, Dan
Multichannel quantum defect theory is adapted to treat simultaneous rotational and vibrational preionization in H2. The strongly preionized spectrum between the N+=0 and N+=2 rotational thresholds of photoionization of H2X1?g+(J?=0, v?=0) to produce H2+X2?g+(N+, v+=0) is computed as example and good agreement is obtained with the photoionization data of Dehmer and Chupka.
Theoretical analysis of the magnetization and of the paramagnetic and diamagnetic magneto-optical effects in Pr-substituted yttrium iron garnets using quantum theory
NASA Astrophysics Data System (ADS)
Yang, Jiehui; Xu, You; Zhang, Fang; Guillot, Maurice
By using quantum theory, the magneto-optical (Faraday rotation, Faraday ellipticity) properties at photon energies below 6 eV and the magnetic properties of the Pr3+ ion in the Y3Fe5O12 garnet are analyzed in the 50-300 K temperature range. The strong enhancement of the Faraday rotation induced by the Pr presence originates mainly from the intraionic electrical dipole transitions between the split 4f2 and 4f5d levels. It is shown that the most important factor is the Pr-Fe superexchange interaction: if there is no Zeeman effect, no magneto-optical (MO) effects exist. The ``paramagnetic'' and ``diamagnetic'' contributions to the MO properties are discussed in detail: if only the Zeeman effect on the ground state is taken into account, the paramagnetic term which is strongly temperature dependent is obtained; on the contrary, if only the Zeeman effect on the excited configuration is considered, the diamagnetic contribution which is temperature insensitive is present. The observed MO properties result from these two components but are mainly determined by the paramagnetic one; the MO resonance frequencies are related to the energies of the multiplets of the ground term and of the excited configuration and to the crystal-field splitting of all these multiplets. Using this approach, the theoretically calculated results of both Pr magnetization and MO effects are in good agreement with experimental data. It is shown that the simultaneous treatment of the magnetic and MO phenomena is a powerful tool to prove the correctness of the approach and of the so-determined parameters. Finally, it is demonstrated that the mixing of the different multiplets of the ground term has a great influence on both magnetic and MO properties.
A quantum mechanical polarizable continuum model for the calculation of resonance Raman spectra in condensed phase
Benedetta Mennucci; Chiara Cappelli; Roberto Cammi; Jacopo Tomasi
In this paper we present two computational strategies to simulate resonance Raman spectra of solvated molecules within the\\u000a framework of the polarizable continuum model (PCM). These two strategies refer to two different theoretical approaches to\\u000a the RR spectra, namely the transform theory and the short-time dynamics. The first is based on the explicit detemination of\\u000a the mimimum geometries of ground
MATLAB-based program for optimization of quantum cascade laser active region parameters and calculation of output characteristics in magnetic field
NASA Astrophysics Data System (ADS)
Smiljani?, J.; Äe×elj, M.; Milanovi?, V.; Radovanovi?, J.; Stankovi?, I.
A strong magnetic field applied along the growth direction of a quantum cascade laser (QCL) active region gives rise to a spectrum of discrete energy states, the Landau levels. By combining quantum engineering of a QCL with a static magnetic field, we can selectively inhibit/enhance non-radiative electron relaxation process between the relevant Landau levels of a triple quantum well and realize a tunable surface emitting device. An efficient numerical algorithm implementation is presented of optimization of GaAs/AlGaAs QCL region parameters and calculation of output properties in the magnetic field. Both theoretical analysis and MATLAB implementation are given for LO-phonon and interface roughness scattering mechanisms on the operation of QCL. At elevated temperatures, electrons in the relevant laser states absorb/emit more LO-phonons which results in reduction of the optical gain. The decrease in the optical gain is moderated by the occurrence of interface roughness scattering, which remains unchanged with increasing temperature. Using the calculated scattering rates as input data, rate equations can be solved and population inversion and the optical gain obtained. Incorporation of the interface roughness scattering mechanism into the model did not create new resonant peaks of the optical gain. However, it resulted in shifting the existing peaks positions and overall reduction of the optical gain. Catalogue identifier: AERL_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERL_v1_0.html Program obtainable from: CPC Program Library, QueenÆs University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 37763 No. of bytes in distributed program, including test data, etc.: 2757956 Distribution format: tar.gz Programming language: MATLAB. Computer: Any capable of running MATLAB version R2010a or higher. Operating system: Any platform supporting MATLAB version R2010a or higher. RAM: Minimum required is 1 GB. Memory usage increases for less intense magnetic fields. Classification: 15. Nature of problem: The nature of the problem is to provide an efficient numerical algorithm implementation for optimization of GaAs/AlGaAs QCL active region parameters and calculation of output properties in the magnetic field. Solution method: The optimization of the QCL laser performance at selected wavelength is performed at entire free-parameters space using simulated annealing algorithm. The scattering rates are calculated in the presence and without magnetic field and used as coefficients in rate equations. The standard MATLAB procedures were used to solve iteratively this system of equations and obtain distribution of electron densities over electronic states. Restrictions: The machine must provide the necessary main memory which decreases roughly quadratically with the increase of the magnetic field intensity. Running time: Optimization time on Intel 3 GHz processor is about 2ū104 s. The calculation time of laser output properties for values set automatically in GUI is 5ū104 s.
Toward 5 V Li-Ion Batteries: Quantum Chemical Calculation and Electrochemical Characterization of Sulfone-Based High-Voltage Electrolytes.
Wu, Feng; Zhou, Hang; Bai, Ying; Wang, Huali; Wu, Chuan
In seeking new sulfone-based electrolytes to meet the demand of 5 V lithium-ion batteries, we have combined the theoretical quantum chemistry calculation and electrochemical characterization to explore several sulfone/cosolvent systems. Tetramethylene sulfone (TMS), dimethyl sulfite (DMS), and diethyl sulfite (DES) were used as solvents, and three kinds of lithium salts including LiBOB, LiTFSI, and LiPF6 were added into TMS/DMS [1:1, (v)] and TMS/DES [1:1, (v)] to form high-voltage electrolyte composites, respectively. All of these electrolytes display wide electrochemical windows of more than 5.4 V, with the high electrolyte conductivities being more than 3 mS/cm at room temperature. It is indicated that to achieve the best ionic conductivity in TMS/DMS cosolvent, the optimized concentrations of lithium salts LiBOB, LiTFSI, and LiPF6 were 0.8, 1, and 1 M, respectively. Furthermore, the vibrational changes of the molecular functional groups in the cosolvents were evaluated by Fourier transform infrared spectroscopy. It is found that lithium salts show strong interaction with the main functional sulfone groups and sulfonic acid ester group, thus playing a vital role in the enhancement of the ionic conductivity and electrochemical stability of the solvent system. These sulfone-based solvents with high electrochemical stability are expected to become a new generation of a high-voltage organic electrolytic liquid system for lithium-ion batteries. PMID:26087246
Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl ? Cl + DF reaction.
Bulut, Niyazi; K?os, Jacek; Roncero, Octavio
We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 - 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance. PMID:26049499
The Open Gate of the KV1.2 Channel: Quantum Calculations Show the Key Role of Hydration
Kariev, AlisherĀM.; Njau, Philipa; Green, MichaelĀE.
The open gate of the Kv1.2 voltage-gated potassium channel can just hold a hydrated K+ ion. Quantum calculations starting from the x-ray coordinates of the channel confirm this, showing little change from the x-ray coordinates for the protein. Water molecules not in the x-ray coordinates, and the ion itself, are placed by the calculation. The water molecules, including their orientation and hydrogen bonding, with and without an ion, are critical for the path of the ion, from the solution to the gate. A sequence of steps is postulated in which the potential experienced by the ion in the pore is influenced by the position of the ion. The gate structure, with and without the ion, has been optimized. The charges on the atoms and bond lengths have been calculated using natural bond orbital calculations, giving K+ ?0.77 charges, rather than 1.0. The PVPV hinge sequence has been mutated inĀsilico to PVVV (P407V in the 2A79 numbering). The water structure around the ion becomes discontinuous, separated into two sections, above and below the ion. PVPV conservation closely relates to maintaining the water structure. Finally, these results have implications concerning gating. PMID:24507595
Characterizing Surface Acidic Sites in Mesoporous-Silica-Supported Tungsten Oxide Catalysts Using Solid State NMR and Quantum Chemistry Calculations
Hu, Jian Z.; Kwak, Ja Hun; Wang, Yong; Hu, Mary Y.; Turcu, Romulus VF; Peden, Charles HF
The acidic sites in dispersed tungsten oxide supported on SBA-15 mesoporous silica were investigated using a combination of pyridine titration, both fast-, and slow-MAS {sup 15}N NMR, static {sup 2}H NMR, and quantum chemistry calculations. It is found that the bridged acidic -OH groups in surface adsorbed tungsten dimers (i.e., W-OH-W) are the Broensted acid sites. The unusually strong acidity of these Broensted acid sites is confirmed by quantum chemistry calculations. In contrast, terminal W-OH sites are very stable and only weakly acidic as are terminal Si-OH sites. Furthermore, molecular interactions between pyridine molecules and the dimer Broensted and terminal W-OH sites for dispersed tungsten oxide species is strong. This results in restricted molecular motion for the interacting pyridine molecules even at room temperature, i.e., a reorientation mainly about the molecular 2-fold axis. This restricted reorientation makes it possible to estimate the relative ratio of the Broensted (tungsten dimer) to the weakly acidic terminal W-OH sites in the catalyst using the slow-MAS {sup 1}H-{sup 15}N CP PASS method.
Complementing high-throughput X-ray powder diffraction data with quantum-chemical calculations: Application to piroxicam form III.
Naelapõõ, Kaisa; van de Streek, Jacco; Rantanen, Jukka; Bond, Andrew D
High-throughput crystallisation and characterisation platforms provide an efficient means to carry out solid-form screening during the pre-formulation phase. To determine the crystal structures of identified new solid phases, however, usually requires independent crystallisation trials to produce single crystals or bulk samples of sufficient quantity to carry out high-quality X-ray diffraction measurements. This process could be made more efficient by a robust procedure for crystal structure determination directly from high-throughput X-ray powder diffraction (XRPD) data. Quantum-chemical calculations based on dispersion-corrected density functional theory (DFT-D) have now become feasible for typical small organic molecules used as active pharmaceutical ingredients. We demonstrate how these calculations can be applied to complement high-throughput XRPD data by determining the crystal structure of piroxicam form III. These combined experimental/quantum-chemical methods can provide access to reliable structural information in the course of an intensive experimentally based solid-form screening activity or in other circumstances wherein single crystals might never be viable, for example, for polymorphs obtained only during high-energy processing such as spray drying or milling. PMID:22886472
Quantum mechanical calculations of vibrational population inversion in chemical reactions - Numerically exact L-squared-amplitude-density study of the H2Br reactive system
NASA Technical Reports Server (NTRS)
Zhang, Y. C.; Zhang, J. Z. H.; Kouri, D. J.; Haug, K.; Schwenke, D. W.
Numerically exact, fully three-dimensional quantum mechanicl reactive scattering calculations are reported for the H2Br system. Both the exchange (H + H-prime Br to H-prime + HBr) and abstraction (H + HBR to H2 + Br) reaction channels are included in the calculations. The present results are the first completely converged three-dimensional quantum calculations for a system involving a highly exoergic reaction channel (the abstraction process). It is found that the production of vibrationally hot H2 in the abstraction reaction, and hence the extent of population inversion in the products, is a sensitive function of initial HBr rotational state and collision energy.
Vibrations and reorientations of NH3 molecules in [Mn(NH3)6](ClO4)2 studied by infrared spectroscopy and theoretical (DFT) calculations.
Hetma?czyk, Joanna; Hetma?czyk, Lukasz; Migda?-Mikuli, Anna; Mikuli, Edward
The vibrational and reorientational motions of NH3 ligands and ClO4(-) anions were investigated by Fourier transform middle-infrared spectroscopy (FT-IR) in the high- and low-temperature phases of [Mn(NH3)6](ClO4)2. The temperature dependencies of full width at half maximum (FWHM) of the infrared bands at: 591 and 3385cm(-1), associated with: ?r(NH3) and ?as(N-H) modes, respectively, indicate that there exist fast (correlation times ?R?10(-12)-10(-13)s) reorientational motions of NH3 ligands, with a mean values of activation energies: 7.8 and 4.5kJmol(-1), in the phase I and II, respectively. These reorientational motions of NH3 ligands are only slightly disturbed in the phase transition region and do not significantly contribute to the phase transition mechanism. Fourier transform far-infrared and middle-infrared spectra with decreasing of temperature indicated characteristic changes at the vicinity of PT at TC(c)=137.6K (on cooling), which suggested lowering of the crystal structure symmetry. Infrared spectra of [Mn(NH3)6](ClO4)2 were recorded and interpreted by comparison with respective theoretical spectra calculated using DFT method (B3LYP functional, LANL2DZ ECP basis set (on Mn atom) and 6-311+G(d,p) basis set (on H, N, Cl, O atoms) for the isolated equilibrium two models (Model 1 - separate isolated [Mn(NH3)6](2+) cation and ClO4(-) anion and Model 2 - [Mn(NH3)6(ClO4)2] complex system). Calculated optical spectra show a good agreement with the experimental infrared spectra (FT-FIR and FT-MIR) for the both models. PMID:25459713
Formation of a thymine-Hg(II)-thymine metal-mediated DNA base pair: proposal and theoretical calculation of the reaction pathway.
Ŗebera, Jakub; Burda, Jaroslav; Straka, Michal; Ono, Akira; Kojima, Chojiro; Tanaka, Yoshiyuki; Sychrovsk², VladimĒr
A reaction mechanism that describes the substitution of two imino protons in a thymine:thymine (T:T) mismatched DNA base pair with a Hg(II) ion, which results in the formation of a (T)N3-Hg(II)-N3(T) metal-mediated base pair was proposed and calculated. The mechanism assumes two key steps: The formation of the first Hg(II)-N3(T) bond is triggered by deprotonation of the imino N3 atom in thymine with a hydroxo ligand on the Hg(II) ion. The formation of the second Hg(II)-N3(T) bond proceeds through water-assisted tautomerization of the remaining, metal-nonbonded thymine base or through thymine deprotonation with a hydroxo ligand of the Hg(II) ion already coordinated to the thymine base. The thermodynamic parameters ?GR =-9.5?kcal?mol(-1), ?HR =-4.7?kcal?mol(-1), and ?SR =16.0?cal?mol(-1) ?K(-1) calculated with the ONIOM (B3LYP:BP86) method for the reaction agreed well with the isothermal titration calorimetric (ITC) measurements by Torigoe et?al. [H. Torigoe, A. Ono, T. Kozasa, Chem. Eur. J. 2010, 16, 13218-13225]. The peculiar positive reaction entropy measured previously was due to both dehydration of the metal and the change in chemical bonding. The mercury reactant in the theoretical model contained one hydroxo ligand in accord with the experimental pKa ?value of 3.6 known for an aqua ligand of a Hg(II) center. The chemical modification of T:T mismatched to the T-Hg(II)-T metal-mediated base pair was modeled for the middle base pair within a trinucleotide B-DNA duplex, which ensured complete dehydration of the Hg(II) ion during the reaction. PMID:23766024
Active layer design and power calculation of nitride-based THz quantum cascade lasers
NASA Astrophysics Data System (ADS)
Chou, HungChi; Anwar, Mehdi; Manzur, Tariq
Room temperature III-nitride QCL THz is reported. With increasing carrier concentration, the peak in optical shifts towards higher energies. Peak in the optical gain increases with carrier concentration demonstrating a blue shift correlated to quantum confinement. THz power increases linearly with current demonstrating an output power of 0.4448 ?W at 6THz. A higher THz power is obtained in AlxGa1-xN/GaN/AlxGa1-x heterostructures as compared to heterostructures incorporating In. An increase in the Al-mole fraction results in higher THz power.
Molecular modeling, theoretical calculations and property evaluation of three muscarinic agonists. X-ray structures of LU 25-109 and WAL 2014
NASA Astrophysics Data System (ADS)
Dolmella, A.; Bandoli, G.; Cavallin, M.
LU 25-109 ( II) and WAL 2014 (talsaclidine, III) are two M1 muscarinic agonists chemically related to the natural substance arecoline ( I). All these compounds have beneficial effects on memory and cognition in animals and humans, and they have been proposed in the treatment of Alzheimer's disease, but only III will likely find a place in therapy. In this work we have investigated the solid state structures of II and III, and the X-ray structures of the two molecules and of the parent compound I have been used to input a series of computational chemistry efforts. In particular, the X-ray geometries have been manipulated to model 20 molecular structures ( 1- 20) which have been submitted to ab initio, semiempirical quantum mechanics and molecular mechanics calculations. The conformational space accessible to the 20 structures has been assessed by means of potential energy maps. The reactivities of 1- 20 have been estimated by examining at the graphics terminal the composition and the extension of the frontier orbitals (HOMOs and LUMOs) and of the molecular electrostatic potential. The information obtained has been interpreted to explain the different degrees of activity shown by I- III. Our data indicate that III has better in vivo activity for its intermediate size, less polar surface, conformational rigidity and orientation of reactive domains.
Tungsten-dependent formaldehyde ferredoxin oxidoreductase: Reaction mechanism from quantum chemical calculations
Liao, Rongzhen
theory Enzyme catalysis Formaldehyde ferredoxin oxidoreductase from Pyrococcus furiosus is a tungsten-ray crystal structure of the native enzyme. Based on the calculations, we propose a new mechanism in which, and the nature of the axial ligands, tungsten enzymes have been divided into three different families: aldehyde
CONTROL OF LASER RADIATION PARAMETERS: Stabilisation of a laser by the calculated quantum transition frequency
NASA Astrophysics Data System (ADS)
Bagaev, S. N.; Dmitriev, A. K.; Lugovoy, A. A.
A method is proposed to stabilise the frequency of a HeŚNe laser with an intracavity nonlinear absorption cell by the calculated frequency of the 7?6 transition of F2(2)P(7)?3 in methane. The long-term frequency stability and reproducibility are measured for a HeŚNe/CH4 laser with a telescopic cavity.
Theoretical Calculations of Mechanical, Electronic, and Chemical Bonding in CaN2, SrN2, and BaN2
NASA Astrophysics Data System (ADS)
Zhang, Li-Qin; Cheng, Yan; Niu, Zhen-Wei; Piao, Chang-Ge; Ji, Guang-Fu
We present a first-principles density functional theory-based study about the impact of pressure on the structural and elastic properties of bulk CaN2, SrN2, and BaN2. Non-spin and spin polarized calculations indicate that the non-spin polarized ground state was more favourable with magnetic moments of 1.049 ?B, 1.059 ?B, and 1.014 ?B for CaN2, SrN2, and BaN2, respectively, and these were in good agreement with previous experimental and theoretical data. The high bulk modulus of CaN2, SrN2, and BaN2 confirm that those compounds have low compressibility and high hardness. The obtained bulk modulus, N-N bond length, and optimized structure parameters are similar to those from previous studies.With an increase in applied pressure the independent elastic constants of CaN2, SrN2, and BaN2 indicated the presence of mechanical instability at 20, 15, and 10 GPa, which is possibly related to phase transitions in addition to a decrease in N-N bond length.
Detection of Structural Changes upon One-Electron Oxidation and Reduction of Stilbene Derivatives by Time-Resolved Resonance Raman Spectroscopy during Pulse Radiolysis and Theoretical Calculations.
Fujitsuka, Mamoru; Cho, Dae Won; Choi, Jungkweon; Tojo, Sachiko; Majima, Tetsuro
Stilbene (St) derivatives have been investigated for many years because of their interesting photochemical reactions such as cis-trans isomerization in the excited states and charged states and their relation to poly(p-phenylenevinylene)s. To clarify their charged state properties, structural information is indispensable. In the present study, radical cations and radical anions of St derivatives were investigated by radiation chemical methods. Absorption spectra of radical ion states were obtained by transient absorption measurements during pulse radiolysis; theoretical calculations that included the solvent effect afforded reasonable assignments. The variation in the peak position was explained by using HOMO and LUMO energy levels. Structural changes upon one-electron oxidation and reduction were detected by time-resolved resonance Raman measurements during pulse radiolysis. Significant downshifts were observed with the CC stretching mode of the ethylenic groups, indicative of the decrease in the bonding order. It was confirmed that the downshifts observed with reduction were larger than those with oxidation. On the other hand, the downshift caused by oxidation depends significantly on the electron-donating or electron-withdrawing nature of the substituents. PMID:26052901
Quantum confinement effect in armchair graphene nanoribbons: Effect of strain on band gap modulation studied using first-principles calculations
NASA Astrophysics Data System (ADS)
Loh, Siow Mean; Huang, Yu-Hui; Lin, Ken-Ming; Su, W. S.; Wu, B. R.; Leung, T. C.
The quantum confinement effect may play an important role in the gap modulation of armchair graphene nanoribbons (AGNRs) under strain. Using the phase accumulation model, we have investigated the energy-dependent phase shift ?(?) at the ? point of AGNRs under various strains using first-principles calculation. The calculation results show that although the energy dispersion of the phase shift is modified by strain, the phase shift near the Fermi level is close to 0.75?, indicating that strain has little effect near that energy level. We can approximate the energy-dependent phase shift by a constant, ?(?)=0.75?, for AGNRs under various x strains. Due to the structural similarity between AGNRs and zigzag carbon nanotubes (ZCNTs), the electronic properties of AGNRs should be similar to those of ZCNTs. The quantization condition of the wave vector of ZCNTs governed by the periodic boundary condition along the circumference direction is similar to that of AGNRs except that the phase shift is equal to zero, ? (?)=0. Using the zone-folding (ZF) method, we can calculate the band gap of any strained AGNR (ZCNT) from the phase shift ?=0.75? (?=0) and the electronic structure of the strained graphene. The AGNR shows a zigzag behavior of the dependence of the band gap on strain which is very similar to the ZCNT. The zigzag patterns are significantly shifted by different phase shifts. The peak value of the band gap and the period of the pattern decreases as the width of the ribbon increases. For a given AGNR, the peak value and the period of the pattern increase as the strain increases. A flattening of the peaks appears at the strain where the maximum band gap occurs due to large compressive strain. All these observations can be understood easily from our ZF calculations. The agreement between our model and real local-density approximation calculations indicates that our model can provide an efficient and accurate method to estimate the band gap of AGNRs and ZCNTs under strain, and therefore can provide a better understanding of the effect of quantum confinement on the electronic properties of AGNRs.
Molecular structure analysis and spectroscopic characterization of 9-methoxy-2H-furo[3,2-g]chromen-2-one with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Swarnalatha, N.; Gunasekaran, S.; Muthu, S.; Nagarajan, M.
Experimental and theoretical investigations on the molecular structure, electronic and vibrational characteristics of 9-methoxy-2H-furo[3,2-g]chromen-2-one (9M2HFC) were presented. The vibrational frequencies were obtained by DFT/B3LYP calculations employing 6-311++G(d,p) basis set, were compared with experimental FT-IR and FT-Raman spectral data. The FT-IR spectrum (4000-400 cm-1) and FT-Raman spectrum (4000-100 cm-1) in solid phase were recorded for 9M2HFC. The geometry of the title compound was fully optimized. Quantum chemical calculations of the equilibrium geometry, the complete vibrational assignments of wavenumbers using potential energy distribution (PED) calculated with scaled quantum mechanics infrared intensities, Raman activities of the title molecule was reported. HOMO-LUMO energies, molecular electrostatic potential, Mulliken population analysis on atomic charges, natural bond orbital (NBO) analysis, non linear optical behavior in terms of first order hyperpolarizability, and thermodynamic properties of the title molecule were carried out. Finally, simulated FT-IR and FT-Raman spectra showed good agreement with the observed spectra.
Calculating solution redox free energies with ab initio quantum mechanical/molecular mechanical minimum free energy path method
Zeng Xiancheng; Hu Hao; Hu Xiangqian; Yang Weitao [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States)
A quantum mechanical/molecular mechanical minimum free energy path (QM/MM-MFEP) method was developed to calculate the redox free energies of large systems in solution with greatly enhanced efficiency for conformation sampling. The QM/MM-MFEP method describes the thermodynamics of a system on the potential of mean force surface of the solute degrees of freedom. The molecular dynamics (MD) sampling is only carried out with the QM subsystem fixed. It thus avoids 'on-the-fly' QM calculations and thus overcomes the high computational cost in the direct QM/MM MD sampling. In the applications to two metal complexes in aqueous solution, the new QM/MM-MFEP method yielded redox free energies in good agreement with those calculated from the direct QM/MM MD method. Two larger biologically important redox molecules, lumichrome and riboflavin, were further investigated to demonstrate the efficiency of the method. The enhanced efficiency and uncompromised accuracy are especially significant for biochemical systems. The QM/MM-MFEP method thus provides an efficient approach to free energy simulation of complex electron transfer reactions.
Studies on vibrational, NMR spectra and quantum chemical calculations of N-Succinopyridine: An organic nonlinear optical material
NASA Astrophysics Data System (ADS)
Kannan, V.; Thirupugalmani, K.; Brahadeeswaran, S.
Single crystals of N-Succinopyridine (NSP) have been grown from water using solution growth method by isothermal solvent evaporation technique. The solid state Fourier Transform Infrared (FTIR) spectrum of the grown crystal shows a broad absorption extending from 3450 down to 400 cm-1, due to H-bond vibrations and other characteristic vibrations. Fourier Transform Raman (FT-Raman) spectrum of NSP single crystal shows Raman intensities ranging from 3100 to 100 cm-1 due the characteristics vibrations of functional groups present in NSP. The proton and carbon positions of NSP have been described by 1H and 13C NMR spectrum respectively. Ab initio quantum chemical calculations on NSP have been performed by density functional theory (DFT) calculations using B3LYP method with 6-311++G(d,p) basis set. The predicted first hyperpolarizability is found to be 1.29 times greater than that of urea and suggests that the title compound could be an attractive material for nonlinear optical applications. The calculated HOMO-LUMO energies show that charge transfers occur within the molecule and other related molecular properties. Molecular properties such as Mulliken population analysis, thermodynamic functions and perturbation theory energy analysis have also been reported. Electrostatic potential map (ESP) of NSP obtained by electron density isosurface provided the information about the size, shape, charge density distribution and site of chemical reactivity of the title molecule. The molecular stability and bond strength have been investigated through the Natural Bond Orbital (NBO) analysis.
Long-range superexchange interaction in copper(II)-dimers: A quantum mechanical calculation
NASA Astrophysics Data System (ADS)
Erasmus, C.; Haase, W.
Self consistent field-M°ller-Plesset (SCF-MP) calculations have been performed to reproduce the experimentally observable exchange interaction J as a function of long distances in Cu-dimers. Four models with different extended bridging ligands were chosen to cover a Cu(II)?Cu(II) separation of ca. 7.0-11.0 ┼. The calculated J values fit the limiting function of R.E. Coffman and G.R. Buettner ( J. Phys. Chem.18, 2387 (1979)] very well. Nevertheless the tendency of the J values was discussed rather than their absolute values. The reasons for the relatively strong measured exchange interaction of 2 J = -140 cm -1 for H = -2 J12S1S2 for the same terephthalato-bridged Cu(II)?Cu(II) dimers with a Cu?Cu separation of 11.25 ┼ were discussed.
Quantum chemistry calculations of 3-Phenoxyphthalonitrile dye sensitizer for solar cells
NASA Astrophysics Data System (ADS)
Kumar, P. Senthil; Vasudevan, K.; Prakasam, A.; Geetha, M.; Anbarasan, P. M.
The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 3-Phenoxyphthalonitrile were studied based on Hartree-Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet-visible (UV-vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to ? ? ?* transitions. Calculated results suggest that the three excited states with the lowest excited energies in 3-Phenoxyphthalonitrile is due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO 2 electrode and dye sensitizer 3-Phenoxyphthalonitrile is due to an electron injection process from excited dye to the semiconductor's conduction band. The role of phenoxy group in 3-Phenoxyphthalonitrile in geometries, electronic structures, and spectral properties were analyzed.
Valence XPS, IR, and C13 NMR spectral analysis of 6 polymers by quantum chemical calculations
NASA Astrophysics Data System (ADS)
Endo, Kazunaka; Ida, Tomonori; Shimada, Shingo; Ortiz, Joseph Vincent; Deguchi, Kenzo; Shimizu, Tadashi; Yamada, Kazuhiko
Valence XPS (VXPS), IR, and C13 NMR spectra of 6 polymers (PE, PS, PMMA, PET, Nylon6, PVC) have been analyzed using the model oligomers from B3LYP/6-31+G(d,p) basis calculations in GAUSSIAN 09. We simulated VXPS of the polymers by the negative of the orbital energies of the ground electronic state at the geometry-optimization of the model oligomers. The simulated VXPS spectra by B3LYP/6-31+G(d,p) basis level were compared with simulated spectra by calculations of SAOP method of ADF program. Simulated IR, and C13 NMR spectra of polymers were obtained from the other SCF calculations of B3LYP/6-31+G(d,p) basis using atomic coordinates of the model molecules at the geometry optimization, in order to gain the vibrational frequencies and nuclear magnetic shielding tensors, respectively. We have clarified the electronic states of the polymers from the good accordance of simulated VXPS, IR, and C13 NMR spectra of polymer models molecules with the experimental ones of the polymers.
Mechanism for Intein C-Terminal Cleavage: A Proposal from Quantum Mechanical Calculations
Shemella, Philip; Pereira, Brian; Zhang, Yiming; Van Roey, Patrick; Belfort, Georges; Garde, Shekhar; Nayak, Saroj K.
Inteins are autocatalytic protein cleavage and splicing elements. A cysteine to alanine mutation at the N-terminal of inteins inhibits splicing and isolates the C-terminal cleavage reaction. Experiments indicate an enhanced C-terminal cleavage reaction rate upon decreasing the solution pH for the cleavage mutant, which cannot be explained by the existing mechanistic framework. We use intein crystal structure data and the information about conserved amino acids to perform semiempirical PM3 calculations followed by high-level density functional theory calculations in both gas phase and implicit solvent environments. Based on these calculations, we propose a detailed ōlow pHö mechanism for intein C-terminal cleavage. Water plays an important role in the proposed reaction mechanism, acting as an acid as well as a base. The protonation of the scissile peptide bond nitrogen by a hydronium ion is an important first step in the reaction. That step is followed by the attack of the C-terminal asparagine side chain on its carbonyl carbon, causing succinimide formation and simultaneous peptide bond cleavage. The computed reaction energy barrier in the gas phase is ?33 kcal/mol and reduces to ?25 kcal/mol in solution, close to the 21 kcal/mol experimentally observed at pH 6.0. This mechanism is consistent with the observed increase in C-terminal cleavage activity at low pH for the cleavage mutant of the Mycobacterium tuberculosis RecA mini-intein. PMID:17085503
Molecular structure and spectroscopic characterization of Carbamazepine with experimental techniques and DFT quantum chemical calculations.
Suhasini, M; Sailatha, E; Gunasekaran, S; Ramkumaar, G R
A systematic vibrational spectroscopic assignment and analysis of Carbamazepine has been carried out by using FT-IR, FT-Raman and UV spectral data. The vibrational analysis were aided by electronic structure calculations - ab initio (RHF) and hybrid density functional methods (B3LYP) performed with standard basis set 6-31G(d,p). Molecular equilibrium geometries, electronic energies, natural bond order analysis, harmonic vibrational frequencies and IR intensities have been computed. A detailed interpretation of the vibrational spectra of the molecule has been made on the basis of the calculated Potential Energy Distribution (PED) by VEDA program. UV-visible spectrum of the compound was also recorded and the electronic properties, such as HOMO and LUMO energies and ?max were determined by HF/6-311++G(d,p) Time-Dependent method. The thermodynamic functions of the title molecule were also performed using the RHF and DFT methods. The restricted Hartree-Fock and density functional theory-based nuclear magnetic resonance (NMR) calculation procedure was also performed, and it was used for assigning the (13)C and (1)H NMR chemical shifts of Carbamazepine. PMID:25682215
Calculating TMDs of an Unpolarized Target: Quasi-Classical Approximation and Quantum Evolution
Yuri V. Kovchegov; Matthew D. Sievert
We set up a formalism for calculating transverse-momentum-dependent parton distribution functions (TMDs) using the tools of saturation physics. By generalizing the quasi-classical Glauber-Gribov-Mueller/McLerran-Venugopalan approximation to allow for the possibility of spin-orbit coupling, we show how any TMD can be calculated in the saturation framework. This can also be applied to the TMDs of a proton by modeling it as a large "nucleus." To illustrate our technique, we calculate the quark TMDs of an unpolarized nucleus at large-x: the unpolarized quark distribution and the quark Boer-Mulders distribution. We observe that spin-orbit coupling leads to mixing between different TMDs of the nucleus and of the nucleons. We then consider the evolution of TMDs: at large-x, in the double-logarithmic approximation, we obtain the Sudakov form factor. At small-x the evolution of unpolarized-target quark TMDs is governed by BK/JIMWLK evolution, while the small-x evolution of polarized-target quark TMDs appears to be dominated by the QCD Reggeon.
Highly Accurate Quantum-Chemical Calculations for the Interstellar Molecules C_3 and l-C_3H^+
NASA Astrophysics Data System (ADS)
Botschwina, Peter; Schr÷der, Benjamin; Stein, Christopher; Sebald, Peter; Oswald, Rainer
Composite potential energy surfaces with coupled-cluster contributions up to CCSDTQP were constructed for C_3 and l-C_3H^+ and used in the calculation of spectroscopic properties. The use of very large AO basis sets and the consideration of higher-order correlation beyond CCSD(T) is of utmost importance for C_3 in order to arrive at quantitative spectroscopic data. The first detection of l-C_3H^+ in the interstellar medium was reported by Pety et al., who attributed 9 radio lines observed in the horsehead photodissociation region to that species. That assignment was questioned by the recent theoretical work of Huang et al. However, our more accurate calculations are well in support of the original assignment. The calculated ground-state rotational constant is B_0 = 11248 MHz, only 0.03% off from the radio astronomical value of 11244.9512▒0.0015 MHz. The ratio of centrifugal distortion constants D_0(exp.)/D_e(theor.) of 1.8 is quite large, but reasonable in comparison with C_3O and C_3. J. Pety, P. Gratier, V. Guzmßn, E. Roueff, M. Gerin et al., Astron. Astrophys. 2012, A68, 1-8. X. Huang, R. C. Fortenberry, T. J. Lee, Astrophys. J. Lett. 2013, 768:L25, 1-5. P. Botschwina, R. Oswald, J. Chem. Phys. 2008, 129, 044305
Structure and vibrational spectra of melaminium bis(trifluoroacetate) trihydrate: FT-IR, FT-Raman and quantum chemical calculations
NASA Astrophysics Data System (ADS)
Sangeetha, V.; Govindarajan, M.; Kanagathara, N.; Marchewka, M. K.; Gunasekaran, S.; Anbalagan, G.
Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted.
Structure and vibrational spectra of melaminium bis(trifluoroacetate) trihydrate: FT-IR, FT-Raman and quantum chemical calculations.
Sangeetha, V; Govindarajan, M; Kanagathara, N; Marchewka, M K; Gunasekaran, S; Anbalagan, G
Melaminium bis(trifluoroacetate) trihydrate (MTFA), an organic material has been synthesized and single crystals of MTFA have been grown by the slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MTFA crystal belongs to the monoclinic system with space group P2/c. The molecular geometry, vibrational frequencies and intensity of the vibrational bands have been interpreted with the aid of structure optimization based on density functional theory (DFT) B3LYP method with 6-311G(d,p) and 6-311++G(d,p) basis sets. The X-ray diffraction data have been compared with the data of optimized molecular structure. The theoretical results show that the crystal structure can be reproduced by optimized geometry and the vibrational frequencies show good agreement with the experimental values. The nuclear magnetic resonance (NMR) chemical shift of the molecule has been calculated by the gauge independent atomic orbital (GIAO) method and compared with experimental results. HOMO-LUMO, and other related molecular and electronic properties are calculated. The Mulliken and NBO charges have also been calculated and interpreted. PMID:24556134
Envelope Function Approximation (EFA) Bandstructure Calculations for III-V Non-square Stepped Alloy Quantum Wells Incorporating Ultra-narrow (ś5┼) Epitaxial Layers
K. A. Kaduki; W. Batty
We describe Envelope Function Approximation (EFA) bandstructure calculations based on a 4-band electron (EL), heavy-hole (HH), light-hole (LH) and split-off hole (SO) effective mass Hamiltonian, with Burt-Foreman hermitianisation, which can handle III-V quantum well structures that incorporate ultra-narrow epi-layers. The model takes into account the coupling of EL, HH, LH and SO bands and is suitable for describing quantum wells
Self-consistent calculation of the electronic structure and electron-electron interaction in self-assembled InAs-GaAs quantum dot structures
L. R. C. Fonseca; J. L. Jimenez; J. P. Leburton; Richard M. Martin
We have performed a detailed self-consistent calculation of the electronic structure and electron-electron interaction energy in pyramidal self-assembled InAs-GaAs quantum dot structures. Our model is general for three-dimensional quantum devices without simplifying assumptions on the shape of the confining potential nor fitting parameters. We have used a continuum model for the strain, from which the position-dependent effective mass and band
Molecular dynamics simulation and quantum chemical calculations for the adsorption of some Azo-azomethine derivatives on mild steel
NASA Astrophysics Data System (ADS)
Shokry, H.
The adsorption mechanism and inhibition performance of some Azo-azomethine derivatives [2-hydroxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene(Azo-1), 2-carboxyphenylazo-2?,4?-dihydroxy-3?-formylbenzene (Azo-II), 2-hydroxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyphenylazomethine}(Azo-I-azomethine I) and 2-carboxyphenylazo-2?,4?-dihydroxy-3?-{2-hydroxyazo methane} (Azo-II-azomethine II) on mild steel at temperatures ranging from 298 K to 333 K have been studied using molecular dynamics (MD) simulation and quantum chemical computational methods. The results obtained revealed that these molecules could effectively adsorb on Fe (0 0 1) surface and the active adsorption sites of these molecules are the nitrogen, oxygen atoms and special negatively charged carbon atoms. All the inhibitors studied had unique corrosion inhibition performance with Azo-II-azomethine II showing the highest inhibition performance at lower temperature ranges from 298 K to 313 K and Azo-II displaying the highest inhibition performance at higher temperature ranges of 323 K and 333 K. Some quantum chemical parameters and the Mulliken charge densities on the optimized structure of inhibitors were calculated using the 6-31?G basis set method to provide further insight into the mechanism of the corrosion inhibition process. The local reactivity was analyzed through the Fukui function and condensed softness indices in order to know the possible sites of nucleophillic and electrophillic attacks.
Benchmark studies of the Bending Corrected Rotating Linear Model (BCRLM) reactive scattering code: Implications for accurate quantum calculations
Hayes, E.F.; Darakjian, Z. (Rice Univ., Houston, TX (USA). Dept. of Chemistry); Walker, R.B. (Los Alamos National Lab., NM (USA))
The Bending Corrected Rotating Linear Model (BCRLM), developed by Hayes and Walker, is a simple approximation to the true multidimensional scattering problem for reaction of the type: A + BC {yields} AB + C. While the BCRLM method is simpler than methods designed to obtain accurate three dimensional quantum scattering results, this turns out to be a major advantage in terms of our benchmarking studies. The computer code used to obtain BCRLM scattering results is written for the most part in standard FORTRAN and has been reported to several scalar, vector, and parallel architecture computers including the IBM 3090-600J, the Cray XMP and YMP, the Ardent Titan, IBM RISC System/6000, Convex C-1 and the MIPS 2000. Benchmark results will be reported for each of these machines with an emphasis on comparing the scalar, vector, and parallel performance for the standard code with minimum modifications. Detailed analysis of the mapping of the BCRLM approach onto both shared and distributed memory parallel architecture machines indicates the importance of introducing several key changes in the basic strategy and algorithums used to calculate scattering results. This analysis of the BCRLM approach provides some insights into optimal strategies for mapping three dimensional quantum scattering methods, such as the Parker-Pack method, onto shared or distributed memory parallel computers.
Peptide Bond Distortions from Planarity: New Insights from Quantum Mechanical Calculations and Peptide/Protein Crystal Structures
Improta, Roberto; Vitagliano, Luigi; Esposito, Luciana
By combining quantum-mechanical analysis and statistical survey of peptide/protein structure databases we here report a thorough investigation of the conformational dependence of the geometry of peptide bond, the basic element of protein structures. Different peptide model systems have been studied by an integrated quantum mechanical approach, employing DFT, MP2 and CCSD(T) calculations, both in aqueous solution and in the gas phase. Also in absence of inter-residue interactions, small distortions from the planarity are more a rule than an exception, and they are mainly determined by the backbone ? dihedral angle. These indications are fully corroborated by a statistical survey of accurate protein/peptide structures. Orbital analysis shows that orbital interactions between the ? system of C? substituents and the ? system of the amide bond are crucial for the modulation of peptide bond distortions. Our study thus indicates that, although long-range inter-molecular interactions can obviously affect the peptide planarity, their influence is statistically averaged. Therefore, the variability of peptide bond geometry in proteins is remarkably reproduced by extremely simplified systems since local factors are the main driving force of these observed trends. The implications of the present findings for protein structure determination, validation and prediction are also discussed. PMID:21949726