We used the USPEX (Universal Structure Predictor: Evolutionary Xtallography) code to obtained the various possible crystal structures for the pyridine…formic acid, pyridazine…formic acid, pyrazine…formic acid and furan…formic acid 1:1 adducts. USPEX has been highly successful in the global search for stable co-crystals of molecules (CSP). At ambient and various pressures, genetic algorithm (GA) based random topological searches were performed to generate the initial structures. Thereafter these large number of structures were relaxed and the total energies of all structures were calculated using first-principles calculation method using Density Functional Theory (DFT) within Perdew-Burke-Ernzerhof (PBE), generalized gradient approximation (GGA) , as implemented in the Vienna Ab-initio Simulation Package (VASP) . Relaxed structures are then ranked with respect to their energies and the lowest 60% of them were subjected to further GA operations like mutation, heredity etc. The new set of structures were again subjected to DFT based optimizations to generate the best structures and the iterations were continued till the structures become invariant towards further modifications. Dispersion corrections were incorporated using the Grimme's empirical D2 method. Recently, it has been shown that computations with the D2 correction provides excellent agreement with the experimental high-pressure crystal-structures. Projector augmented wave (PAW) method was employed to describe the electron-ion interactions. Plane wave kinetic energy cut-off was set to 600 eV in our calculation. The reciprocal-space resolution was sampled for k-points generation (units: 2πÅ -1 ) as 0.16, 0.14, 0.12, 0.10, and 0.09. The crystal structures were visualized using the VESTA software. Molecular level insights into the local chemical environment was evaluated using the molecular quantum chemistry calculations. Energy Decomposition Analysis (EDA) were performed by Amsterdam Density Functional (ADF) program 59 at B3LYP/TZ2P/ZORA level of theory. To account the middle range dispersion interaction energy, Grimme's dispersion correction was employed. The net interaction energy (∆Eint) between the acid and the base was decomposed into Pauli repulsion energy (∆EPauli) between the electrons of same spin, electrostatic interaction energy (∆Eelstat) corresponding to the quasi-classical electrostatic interaction between unperturbed charge distribution of two fragments, orbital interaction energy (∆Eorb) due to the mixing of orbitals, polarization and charge transfers between the chosen fragments and dispersion energy (∆Edisp) due to van der Waals interactions between the fragments. The penetration index was calculated by the Alvarez's model. Standard sets of covalent and van der Waals 63 radii were used for this calculation. The lowest enthalpy structures for the 1:1 complex at 0 GPa for pyridine…formic acid, pyridazine…formic acid, pyrazine…formic acid and furan…formic acid are reported in Fig. .