The i, j are pair of atoms/systems, R ij is the distance between i and j, C n are dispersion coefficients arising from dipole-dipole (n=6), dipole-quadruple (n=8), quadruple-quadruple (n=10) interactions. In general, the dispersion energy is not pair-wise additive because of the many-body effects. Widely utilized methods for dispersion corrections as Grimme's -D2, -D3 10 uses semi-empirical parameters. On the other hand, Tkatchenko-Scheffler method captures the electronic many-body effects to some extent by defining the electron density based Hirshfeld screening of polarizabilities. Both of these methods has been employed successfully for large molecular systems. The other way of introducing the vdW correction is through quantum Drude oscillator (QDO) model which is a quantum harmonic oscillators with two equal and opposite charges tagged at two ends. As a result, two QDOs interact between themselves through Coulomb interactions. This model has been successfully employed to capture long-range interaction between atoms. In particular, dispersion interaction in anionic water-clusters, vibrational spectroscopy in charges water clusters, as a precursor in force-field development, simulating polarizable molecular ionic-liquid and water-lipid interface have been investigated using QDO. Many-Body Dispersion (MBD) method 5 has been another direction where QDO finds its use. In this method, the long-range quantum fluctuations of each atom is modeled by a QDO. The oscillators' polarizabilities have been set to the screened polarizabilities. The dipole-coupled interaction energy between these oscillators therefore provides the interaction energy which is equivalent to random phase approximation (RPA) of correlation energy. Since this model allows for an exact diagonalization of the interaction matrix, it captures many-body effects of all orders. On the other hand, molecular fragmentation techniques have been developed to reduce computational costs for large molecules. Upon fragmentation, a large composite system can be divided into small sub-systems. Thereafter, the results of the high-level calculations on small fragment can be assembled to the desired properties of the large system. Conventional fragment-based methods to calculate the energy of the system can be categorized broadly as overlapping or top-down approach (based inclusion-exclusion principle) and nonoverlapping or bottom-up approach (based on many-body expansion).