Density functional theory studies of hydrostatic compression of crystalline ammonium perchlorate

A detailed study of the structural, electronic, and vibrational properties of crystalline ammonium perchlorate (AP) under hydrostatic compression was performed with density functional theory. The results show that the compressibility of AP is nearly isotropic. Our calculated cell volumes under compression are in agreement with experimental data. As the pressure increases, the band gap of AP. first increases, peaks, and then gradually decreases. An analysis of density of states shows that the interactions between electrons, especially for the valence electrons, are strengthened under the influence of pressure. The calculated vibrational frequencies under different pressures are in agreement with available experimental data. On the whole, the frequency increase is more pronounced in the low-pressure range compared to the high-pressure region, and furthermore, different vibrational modes show distinctly different pressure-dependent behaviors.