Ab initio molecular dynamics simulations study on initial decompositions of β‐HMX at high temperature coupled with high pressures

We performed ab initio molecular dynamics simulations to investigate initial decomposition mechanisms and subsequent chemical processes of β‐HMX (cyclotetramethylene tetranitramine) (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) crystals at high temperature coupled with high pressures. It was found that the initial decomposition step is the simultaneous C–H and N–NO₂ bond cleavage at 3,500 K. When the pressure (1–10 GPa) is applied, the first reaction steps are primarily the C–N and C–H bond fission at 3,500 K. The C–H bond cleavage is a triggering decomposition step of the HMX crystals at 3,500 K coupled with 16 GPa. This indicates that the C–H bonds are much easier to be broken and the hydrogen radicals are much more active. The applied pressures (1–10 GPa) accelerate the decompositions of HMX at 3,500 K. The decomposition pathways and time evolution of the main chemical species demonstrate that the temperature is the foremost factor that affects the decomposition at high pressures (1–10 GPa). However, the decomposition of HMX is dependent on both the temperature (3,500 K) and the pressure (16 GPa). This work will enrich the knowledge of the decompositions of condensed energetic materials under extreme conditions.