A non-empirical intermolecular force-field for trinitrobenzene and its application in crystal structure prediction

An anisotropic atom–atom distributed intermolecular force-field (DIFF) for rigid trinitrobenzene (TNB) is developed using multipole moments, dipolar polarizabilities, and dispersion coefficients derived from the charge density of isolated molecule. The short-range parameters are fitted to first- second-order symmetry-adapted perturbation theory dimer interaction energy calculations density-overlap model guide parameterization anisotropy. used fitting damping long-range polarization also relaxing isotropic in final model, DIFF-srL2(rel). We assess accuracy unrelaxed DIFF-srL2(norel), its equivalent without anisotropy, DIFF-srL0(norel), as these models easier derive. potentials contrasted with empirical repulsion–dispersion organic crystal structures multipoles iterated stockholder atoms (ISAs), FIT(ISA,L4), Gaussian Distributed Analysis (GDMA) multipoles, FIT(GDMA,L4), commonly modeling crystals. tested their ability solid state TNB. non-empirical provide more reasonable relative lattice energies three polymorphs TNB propose sensible hypothetical than (FIT). DIFF-srL2(rel) successfully has most stable structure one many that match coordination sphere form III. neglect conformational flexibility nitro-groups a significant approximation. This methodology provides step toward force-fields capable representing all phases molecule molecular dynamics simulations.