First-principles study of structural stabilities, and electronic and optical properties ofCaF2under high pressure

Abstract

An investigation into the structural stabilities and the electronic and optical properties of $\mathrm{Ca}{\mathrm{F}}_{2}$ under high pressure was conducted using first-principles calculations based on density functional theory. Our results demonstrate that the sequence of the pressure-induced phase transition of $\mathrm{Ca}{\mathrm{F}}_{2}$ is the fluorite structure $(Fm3m)$, the $\mathrm{Pb}{\mathrm{Cl}}_{2}$-type structure $(Pnma)$, and the ${\mathrm{Ni}}_{2}\mathrm{In}$-type structure $(P{6}_{3}∕mmc)$. At these phase transformations, the coordination number of ${\mathrm{Ca}}^{2+}$ increases from eight to nine and then to eleven. The mechanisms of the structure change were revealed from the $\mathrm{Pb}{\mathrm{Cl}}_{2}$-type phase to the ${\mathrm{Ni}}_{2}\mathrm{In}$-type phase. The energy band gap increases with pressure in the $Fm3m$ and the $Pnma$ phases, but decreases in the $P{6}_{3}∕mmc$ phase. The band gap pressure coefficients were obtained using a linear pressure-dependent fit function. In addition, the energy band overlap metallization does not occur up to $218\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The static dielectric constants ${\ensuremath{\epsilon}}_{0}$ vs pressure are also discussed.