First-Principles Molecular Dynamics Study of the Thermal Decomposition Mechanism of TNT

The prolonged and widespread use of 2,4,6-trinitrotoluene (TNT, C₇H₅N₃O₆) has prompted in-depth investigations into its thermal decomposition mechanism. Although considerable research has been conducted on the thermodynamic properties of TNT and other polynitro organic compounds, their thermal stability remains a critical challenge in engineering applications. This study systematically investigates the sequential reaction mechanism of TNT thermal decomposition through first-principles molecular dynamics (FPMD) simulations, revealing three distinct stages: (1) initial solid-phase decomposition, (2) radical generation and carbon cluster formation, and (3) stabilization of final gaseous products, with 157 intermediate species identified. Systematic analysis of functional group evolution revealed three dominant reaction pathways: (i) methyl oxidation-carboxylation, (ii) nitro elimination, and (iii) dimer-mediated methyl elimination. Notably, we observed that nitro-to-nitrito isomerization (C-NO₂ → C-ONO) occurs as a result of the continued oxidation of the benzene ring after C-NO₂ bond cleavage. Kinetic and thermodynamic analyses showed that the direct attack of the oxygen atom on the aromatic ring in path b exhibited the best kinetic advantage in the functional group elimination reaction, while the choice of the initial oxidation site determined the overall decomposition rate.