External Electric Field-Induced Phase Transition of a Series of Energetic Pentazole Crystals: A First-Principles Study

Abstract

A first-principles study was performed to investigate the gradient rule of crystal and electronic features, nonbonded 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 the occupied orbitals to empty ones for (N2H5)+N5 – and (NH3OH)+N5 –, while making it more difficult for that for (NH4)+N5 –. The discussion on intermolecular interactions shows that the rearrangement and the change in the hydrogen bond network occurred. Besides, external electric field could enhance the hydrogen bond interactions for (N2H5)+N5 –, while it could weaken the hydrogen bond interactions for (NH3OH)+N5 – and (NH4)+N5 –. The analysis on vibrational properties reveals that most vibrational modes present redshift for all pentazole crystals. Our findings lay the theoretical foundation for the application of energetic pentazole materials under extreme conditions.