Structural, bonding, and electronic properties of IIA-IV antifluorite compounds

Abstract

We have studied the electronic and structural properties of the antifluorite compounds ${\mathrm{Mg}}_{2}$X (X=Si, Ge, Sn), ${\mathrm{Be}}_{2}$C, and hypothetical compounds ${\mathrm{Mg}}_{2}$C and ${\mathrm{Be}}_{2}$Si using the first-principles pseudopotential total energy method. Five of the compounds are small-gap semiconductors, while ${\mathrm{Be}}_{2}$Si is a metal. Calculated lattice constants agree well with experiment for the four known compounds, but are consistently a few percent smaller than the reported values. The bulk moduli of this group of materials follow a semiempirical formula for ${\mathit{B}}_{0}$ to within \ensuremath{\sim}5%. Bulk moduli calculated from first principles, corrected for the underestimation of the lattice constant, agree well with the available experimental values.