Structural disorder driven component dependent decomposition pathways and intermolecular interactions in HMX/1,4-PDCA...

Structural disorder in energetic cocrystals is known to influence their decomposition behavior, yet the underlying trends remain largely unexplored. In this work, the early-stage decomposition pathways and intermolecular interactions of both crystalline and amorphous HMX/1,4-PDCA cocrystals are investigated via ab initio molecular dynamics simulations at 2500 K. Hirshfeld surface analysis reveals that the intermolecular environment in the selected amorphous model experiences greater strain, characterized by fewer O⋯H contacts alongside increased O⋯O and N⋯O interactions, thereby influencing the decomposition behavior. In both simulated models, the decomposition was initiated by the breakdown of HMX; however, the dominant initiation pathway varies with molecular packing. Specifically, the crystalline model decomposes via H-dissociation, whereas the selected amorphous model preferentially undergoes nitro group dissociation. Under the present simulation conditions, structural disorder is observed to exhibit a component-dependent effect, favoring HMX decomposition while simultaneously inducing more complex and heterogeneous degradation behavior in 1,4-PDCA. The selected amorphous system exhibits higher initial potential energy, faster fragmentation, and enhanced atomic mobility, all suggesting accelerated decomposition kinetics. In contrast, the crystalline model shows a more gradual decomposition process and reaches a lower final potential energy, suggesting a more thermodynamically favorable decomposition pathway. Collectively, these findings provide valuable insights into the role of structural disorder in modulating intermolecular interactions and decomposition mechanisms in energetic cocrystals.