We have explored the degree to which an intermolecular potential for the explosive hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) (J. Phys. Chem. B 1997 101, 798) is transferable for predictions of crystal structures (with the approximation of rigid molecules) of a similar chemical system, in this case, polymorphic phases of the 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) crystal. Molecular packing and isothermal-isobaric molecular dynamics calculations performed with this potential reproduce the main crystallographic features of the epsilon-, beta-, and gamma-HNIW crystals. Thermal expansion coefficients calculated using the present model predict near isotropic expansion for the epsilon- and gamma-HNIW crystal phases and anisotropic expansion for beta-HNIW.