A first-principles study was performed to investigate the gradient rule of crystal and electronic features, non-bonded interactions, and vibrational characteristics of series of energetic pentazole crystals (N₂H₅)⁺N₅⁻, (NH₃OH)⁺N₅⁻, and (NH₄)⁺N₅⁻ under external electric fields. It is found that phase transition of (N₂H₅)⁺N₅⁻ occurred at 0.006 a.u. and that of (NH₄)⁺N₅⁻ occurred at 0.01 a.u., and the phase transition are reflected in almost all properties of these energetic pentazole crystals. The analysis on electronic structure indicates that external electric field could make it easier for electrons to transition from occupied orbitals to empty ones for (N₂H₅)⁺N₅⁻ and (NH₃OH)⁺N₅⁻, while make it more difficult for that for (NH₄)⁺N₅⁻. The discussions on intermolecular interactions show that the rearrangement and the change of hygrogen bond network occurred. Besides, external electric field could enhance the hydrogen bond interactions for (N₂H₅)⁺N₅⁻, while weaken the hydrogen bond interactions for (NH₃OH)⁺N₅⁻ and (NH₄)⁺N₅⁻. The analysis on vibrational properties reveals that most vibrational modes present red shift for all pentazole crystals. Our findings lay the theoretical foundation for the application of energetic pentazole materials under extreme conditions.

Xiaowei Wu

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