A molecular dynamics study of 1,1-diamino-2,2-dinitroethylene (FOX-7) crystal using a symmetry adapted perturbation theory-based intermolecular force field.

A dimer potential energy function for 1,1-diamino-2,2-dinitroethylene (FOX-7) has been developed using symmetry adapted perturbation theory based on a Kohn-Sham density functional theory description of the monomers [SAPT(DFT)]. Interaction energies of 1008 dimer configurations were computed in an augmented double zeta basis set and fitted to an atom-atom intermolecular potential energy function of Coulomb plus Buckingham exp-6 form. The potential was used in isothermal-isostress molecular dynamics simulations to study the structure and thermal/pressure response of FOX-7 crystal. The simulated structure is in very good agreement with experiment and the computed thermal/pressure response of the crystal shows significant anisotropy with respect to crystallographic direction, in-line with experimental observations. It is concluded that SAPT(DFT) is an excellent method for development of intermolecular potentials for energetic molecular crystals.