Initial Decomposition Mechanism of NH₃OH⁺N₅^- Crystal under Thermal and Shock Loading: A First-Principles Study

NH₃OH⁺N₅^- is a novel energetic material (EM) which has attracted much interest for its promising performances, including high energy density, high density, low sensitivity, and low toxicity. In this study, the initial decomposition mechanism of NH₃OH⁺N₅^- crystal was investigated under thermal and shock loading by molecular dynamics simulation. First, programmed heating and constant temperature simulations were carried out by molecular dynamics simulation on the basis of density functional theory (DFT-MD). Results indicated that the initial decomposition reactions of NH₃OH⁺N₅^- could be described by three reactions: proton transfer, ring-opening reaction, and cation decomposition and recombination, and three pathways of ring-opening reaction were found, including the ring-opening of N₅^-, HN₅, and H₂N₆. The first two reactions are the main pathways that produce N₂ molecules. Furthermore, we carried out DFT-MD simulations to study the shock decomposition behaviors of NH₃OH⁺N₅^-, and three initial steps were proposed: N₅^-, HN₅, and N₆ ring-opening. The fewer N₅^- and HN₅ ring-opening reactions were found during the shock simulation, accompanied by a significant change in the N₅^- bond angle. What's more, the transition states of decomposition reactions were investigated through quantum chemical calculations. The results revealed that the proton transfer reaction exhibits lower activation barriers compared to ring-opening reactions, and proton transfer would accelerate ring-opening reactions. In addition, the ring-opening reaction is the main energy-releasing reaction in the early stages of the decomposition. This work could promote the comprehension of the decomposition mechanism and energy release regularity of N₅^- ions.