Electronic and optical properties of the antifluorite semiconductors Be 2C and Mg 2X ( [formula omitted], Si, Ge) under hydrostatic pressure

Abstract

We report on first-principles studies of pressure effect on the electronic and optical properties of the antifluorite compounds Be 2C and Mg 2X ( X = C , Si, Ge) using the full-potential linearized augmented plane wave method within the local density approximation. The minimization of the total energy gives the structural parameters which are in good agreement with the experimental data. The first order bandgap pressure coefficients a Γ – Γ and a Γ – L are positive, while a Γ – X is negative except for the carbide compounds. The smaller values of the coefficients in Be 2C compared to diamond are attributed to the ionic character of the Be–C bond. The structures in the optical spectra shift towards higher energies when the pressure increases. The static dielectric function decreases with pressure for the semiconducting phase.