Electronic and optical properties of the antifluorite semiconductors Be2C and Mg2X (X=CX=C, Si, Ge) under hydrostatic pressure

We report on first-principles studies of pressure effect on the electronic and optical properties of the antifluorite compounds Be2C and Mg2X (X=CX=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 aΓ–ΓaΓ–Γ and aΓ–LaΓ–L are positive, while aΓ–XaΓ–X is negative except for the carbide compounds. The smaller values of the coefficients in Be2C 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.