Electronic and optical properties of alkali metal selenides in anti-CaF2 crystal structure from first-principles

We have performed FP-LAPW calculations in the framework of density functional theory (DFT) to compute ground-state electronic and optical properties of alkali metal selenides M2Se [M: Li, Na, K, Rb] in anti-CaF2 crystal structure. The generalized gradient approximation (GGA) parameterization schemes proposed by Wu and Cohen (WC) and Engel and Vosko (EV) have been utilized for these calculations and some trends in the electronic properties of alkali metal selenides have been analyzed in the light of available theoretical and experimental data of other group IA–VI crystals. Electronic density of states for these compounds has been obtained to elucidate contribution from different anion and cation states to the electronic structure. Optical properties such as complex dielectric function ɛ(ω), absorption coefficient I(ω), refractive index n(ω), extinction coefficient k(ω) and reflectivity R(ω) for incident photon energy up to 35 eV and energy-loss functions have been predicted for M2Se compounds. Various interband transitions and the possible contributions of the cation and anion states to these transitions have been presented.