β → δ phase transition and initial decomposition of HMX nanoparticle from reactive molecular dynamics simulations

We employed ReaxFF molecular dynamics (MD) to simulate the physicochemical properties of HMX nanoparticle at low temperatures. As the temperature increases, its physical and chemical properties change accompanying some transition, which is not reported by any previous studies. The Poisson Scoring Model was used to count phase transition. It is found that the number of the beta- to delta-HMX conformational transition at 458 K is higher than that at other temperatures. The types of decomposition products of the HMX nanoparticle at low temperatures are the same as those by pervious high-temperature experiments and theoretical simulations. The decomposition of the HMX nanoparticle is triggered by the C-H bond dissociation. Its decomposition includes two steps. The one is the decay of the HMX molecules, which is called the direct influence of the solid phase; the other one is the second reaction of small intermediate in less condensed phase. Moreover, the temperature will deeply affect the duration of each stage.