Simulations of High-Pressure Phases in RDX

Using a fully flexible molecular potential in equilibrium molecular dynamics simulations, we study the α- and γ-polymorphs of the energetic molecular crystal hexahydro-1,3,5-trinitro-s-triazine (RDX), their respective properties, and the conditions that contribute to the stress-induced γ → α solid-solid phase transition mechanisms. We find the pressure-dependent atomic structure, mechanical properties, and transition behavior to be described reasonably well. Uniaxial deformation of α-RDX along the crystal axes is shown to result in three different crystal responses where compression of the c-axis results in the α → γ transition, compression of the b-axis causes a transition with resulting structure similar to stacking faults observed by Cawkwell et al. J. Appl. Phys. 2010, 107, 063512, and no transitions are observed for compression of the a-axis.