A TRANSFERABLE INTERMOLECULAR POTENTIAL FOR NITRAMINE CRYSTALS

We have investigated the transferability of a Buckingham repulsion-dis persion intermolecular potential previously developed [J. Phys. Chem. B 1997, 101, 798] for the explosive hexahydro-1,3,5-trinitro-1,3,5-s-t riazine (RDX) to predict the crystal structures (within the approximat ion of rigid molecules) of 30 nitramines, comprising acyclic, monocycl ic, and polycyclic molecules. It is shown that this potential model ac curately reproduces the experimentally determined crystallographic str uctures and lattice energies of these crystals. For the majority of th ese crystals, the best agreement with experiment is obtained when the electrostatic charges are determined using ab initio methods that incl ude electron correlation effects, namely, MP2 and B3LYP. The use of th e electrostatic charges calculated at the Hartree-Fock level results i n large deviations of the predicted lattice energies from the experime ntal values. These deviations of the lattice energies can be significa ntly decreased, without significantly affecting the predicted crystall ographic parameters, by scaling the electrostatic charges with a const ant factor.