Phase Transitions and Mechanical Properties of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine in Different Crystal Phases by Molecular Dynamics Simulation

Abstract

The phase transitions and mechanical properties of the energetic material octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in three pure polymorphs crystals, α-, β-, and δ-phases, have been studied theoretically. Isothermal−isobaric molecular dynamics (MD) simulations were performed in the temperature range of (5 to 555) K at 0 GPa and the pressure range of (0 to 40) GPa at 298 K. The lattice parameters and volumes show nonlinear dependence on the temperature and pressure. In the high-temperature regime, there exist two phase transitions, that is, from β- to α-HMX at 360 K and from α- to δ-HMX at 440 K. Under high pressure, the β-HMX transition to δ-HMX is shown at 27 GPa and 298 K. Within the range of temperature and pressure studies, it can be deduced that the β-HMX at lower temperatures and higher pressures, the α-HMX at higher pressures, and the δ-HMX at lower temperatures have better malleability.