Quantum mechanics insights into the early pyrolysis mechanism of 3,4-dinitro-1H-pyrazole in the amorphous model

Abstract

Self-consistent charge density-functional tight binding molecular dynamics simulations reveal distinct thermal decomposition pathways between crystalline and amorphous 3,4-dinitro-1H-pyrazole (DNP). Key findings include prolonged equilibrium in amorphous systems and dominant NO₂/H dissociation mechanisms. Results show that the potential energy evolution of the crystalline model is similar to that of the amorphous model, in which the amorphous model shows a longer equilibrium stage. Four important decomposition reactions were identified, including NO2 dissociation, H dissociation, H attacking the nitro group, and N-N bond cleavage. The former two reactions are dominant in the decomposition of DNP, and the dissociation of 1-position hydrogen and 3-position nitro group is easier, which is also supported by quantum chemical calculations. For the ring-opening reaction, there is small difference between the two models, primarily involving the N-N bond breakage and C-N bond cleavage to form N2. In addition, more hydrogen dissociation reactions occur in the crystalline model, therefore, DNP in the crystalline model is more likely to decompose, and the products are generated earlier than the amorphous model. These results contribute to our understanding of thermal decomposition of energetic materials with layered structure.