Valence energies for crystalline C, Si, Ge, and Sn with diamond structures have been determined using an ab initio approach based on information from cluster calculations. Correlation contributions, in particular, have been evaluated in the coupled-electron-pair approximation, by means of increments obtained for localized bond orbitals and for pairs and triples of such bonds. Combining these results with corresponding Hartree-Fock (HF) data, we recover about 95% of the experimental cohesive energies. Lattice constants are overestimated at the HF level by about 1.5%; correlation effects reduce these deviations to values which are within the error bounds of this method. A similar behavior is found for the bulk modulus: the HF values which are significantly too high are reduced by correlation effects to ∼97% of the experimental values.

• Received 21 October 1994

DOI:https://doi.org/10.1103/PhysRevB.51.10572