Regulation of early-stage decomposition mechanisms of HMX (Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) by molecular charging

HMX is a representative nitramine energetic material whose decomposition mechanisms under various ignition stimuli have been extensively investigated, primarily for electronically neutral molecules. However, under practical conditions such as laser irradiation, electrostatic discharge or friction, HMX may experience transient electron removal or accumulation. Experimental observations suggest that early-stage decomposition can be influenced by electron-rich or electron-deficient environments, although the underlying mechanisms remain unclear. In this work, the initial unimolecular decomposition mechanisms of HMX are systematically investigated under neutral, positively and negatively charged states using density functional theory combined with the CI-NEB method. Seven representative reaction pathways are examined, including N–NO₂ dissociation, HONO elimination, ring opening, rearrangement and fragmentation. The results show that charging not only lowers the energetic barriers of early decomposition steps but also alters the preferred sequence of bond-breaking and bond-forming events. Negative charging facilitates N–NO₂ dissociation and C–N bond cleavage within the ring, enabling competing ring-opening and multistep rearrangement pathways that are unfavorable in the neutral state. In contrast, positive charging promotes hydrogen-transfer-assisted processes, favoring HONO elimination and related rearrangements. The structural flexibility of HMX is further amplified under charged conditions, giving rise to a more complex and diverse reaction network. Overall, these findings demonstrate how charging reshapes the early decomposition landscape of HMX and offer molecular-level insight into charge-related experimental observations.