Internal standard-assisted ab initio MD simulation for comparative thermal stability and decomposition mechanisms of energetic materials

Thermal stability is one of the most important and fundamental properties of energetic molecules, and still suffers from many challenges in theoretical evaluation prior to experiment determination. This work introduces a novel strategy combining an internal standard method with ab initio molecular dynamics (MD) simulations to overcome the challenges. The proposed approach is validated using five pairs of energetic molecules with different molecular structures and experimental thermal stability. That is, in MD simulations, the molecule that decomposes first with higher frequency in each pair always corresponds to a lower decomposition barrier. This strategy can overcome the issues of the serious temperature fluctuations in ab initio MD simulations, the significant dependence of molecular reaction MD simulation on force field accuracy, and empirical speculation or tedious trial-and-error deduction of thermal decomposition mechanism in static QC calculations. Therefore, it will facilitate to more accurate prediction of thermal stability and decomposition mechanisms of energetic molecules, in particular for those that have not been synthesized yet.