Effect of Pressure on the Optical Properties of Cubic-BaF^sub 2^ Scintillator Crystal: A First-Principles Investigation Using the Modified Becke-Johnson Potential

In this paper, the variation with hydrostatic pressure of some optical properties of the cubic-BaF2 scintillator crystal, including the dielectric function, the energy loss function, and the refractive index, has been studied. The calculations were performed using the full potential linear augmented plane waves (FP-LAPW) method based on density functional theory (DFT). The modified Becke-Johnson potential was selected for the exchange-correlation potential. It is shown that this potential can correctly predict the band gaps and optical properties of the BaF2 compound. The results show that the effect of pressure on the optical properties of BaF2 is quite remarkable in the energy range of 10-22 eV, while the static dielectric constant and static refractive index vary linearly with increasing the pressure. Our calculations show that the peaks in the imaginary part of the dielectric function shift toward higher energies with increasing the pressure and are mainly related to the electronic transitions from F-2p and Ba-5p orbitals to the conduction band. Furthermore, we show that the peaks of the energy loss function, particularly the plasmon frequency, shift to higher energies with increasing pressure.