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

We have studied the electronic and structural properties of the antifluorite compounds Mg[sub 2][ital X] ([ital X]=Si, Ge, Sn), Be[sub 2]C, and hypothetical compounds Mg[sub 2]C and Be[sub 2]Si using the first-principles pseudopotential total energy method. Five of the compounds are small-gap semiconductors, while Be[sub 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 [ital B][sub 0] to within [similar to]5%. Bulk moduli calculated from first principles, corrected for the underestimation of the lattice constant, agree well with the available experimental values.