Structural stabilities, electronic and optical properties of CaF2 under high pressure: A first-principles study

The structural stabilities, electronic and optical properties, the pressure-induced metallization for CaF2 have been studied by using the density functional theory calculations. The ground Fm3¯m phase is predicted to transform into Pnma structure at 8.1 GPa, which is well consistent with the experimental findings. Above 278 GPa, Pnma-CaF2 transform into P63/mmcP63/mmc phase. The calculated structural data for Fm3¯m and pnma phases are in very good agreement with experimental values. The electronic band structures show that Pnma   and P63/mmcP63/mmc phases of CaF2 are insulators at the transition pressure. Upon further compression, the band gap of P63/mmcP63/mmc decreases with pressure, and CaF2 is predicted to undergo metallization around 2250 GPa. The possible reason for the metallization was discussed. All CaF2 polymorphs have ionic character between Ca–F bond with the analysis of the charge–density distribution and density of states.