Coupling of temperature with pressure induced initial decomposition mechanisms of two molecular crystals: An ab initio molecular dynamics study

Ab initio molecular dynamics simulations were performed to study the initiation of decomposition and formation of first products of two molecular crystals pentaerythritol tetranitrate (PETN) and 5-nitro-2,4-dihydro-1,2,4-triazole-3-one (NTO) under thermal decomposition temperature (475 K for PETN and 531 K for NTO) coupled with different pressures (1-5 GPa). The pressure effects on the initial decomposition steps and initially generated products on PETN and NTO were very different. PETN was triggered by C-H a <-O intermolecular hydrogen transfer. The initial decomposition mechanism was independent of the pressure. For NTO, two different initial decomposition mechanisms were found. At 1, 2, and 3 GPa, it was triggered by N-H a <-O intermolecular hydrogen transfer, while at 4 and 5 GPa, it was triggered by N-H a <-N intermolecular hydrogen transfer. This indicates that the initial decomposition mechanism was dependent on the pressure. Our study may provide new insights into initial mechanisms and decomposition reactions of molecular crystal explosives under thermal decomposition temperature coupled with different pressures with details at atomic level.