Evolution of Crystal Structures and Electronic Properties for Ir₂P under High Pressure

The crystals of Ir₂P were predicted under the pressure ranging from 0 to 100 GPa using the CALYPSO structure exploration technique with the first-principles method based on the density functional theory. The predicted physical properties and crystal structures were examined in detail. At ambient pressure, the predicted α-Ir₂P phase was found to have a cubic structure with Fm3m space group, which is consistent with the experimental structure. The pressure-induced structural transformations were unraveled, from the α-Ir₂P phase to the β-Ir₂P phase at 86.4 GPa. The predicted β-Ir₂P phase has I4/mmm space group. In the process of phase transition, the volume of the crystal collapses and a discontinuous first order phase transition occurred. The calculation of the electronic properties showed that the predicted conduction bands and the valence bands of the β-Ir₂P phase overlap near the Fermi surface at 86.4 GPa, indicating that the structure of the β-Ir₂P phase has metallic properties. The electron localization function revealed that the β-Ir₂P phase has a polar covalent bond, a metallic bond and an ionic bond. The Bader charge transfer calculations showed that each P atom transfers 0.19e to Ir atom, mainly due to the strong electronegativity of the Ir atoms.