Structural transformation of energetic cyclo-pentazolate salt under the pressure

The density functional theory (DFT) was applied to investigate the structure, optical properties, and non-bonded interactions of the cyclo-pentazolate salt [Mg(H2O)6(N5)2]·4H2O in the pressure range of 0–100 GPa. The results show that there is a structural transition at the pressure of 64 GPa, which has not been found in the experiments. As the pressure increases, the band gap gradually decreases with a sudden increase at the structural transition point. The analysis of DOS presents that the electronic localization in the crystal gradually weakens under the pressure. The structural transition point also exists in the hydrogen bonds and the Hirshfeld surfaces under compression. The absorption spectra of the cyclo-pentazolate salt at high pressures show some strong bands in the fundamental absorption region. The increasing pressure helps to improve the photoelectric performances of the crystal. Our studies are expected to provide a new understanding of the structural transition of the novel energetic materials under high pressures.