A correlatedab initiotreatment of the zinc-blende wurtzite polytypism of SiC and III - V nitrides

Abstract

Ground-state properties of SiC, AlN, GaN and InN in the zinc-blende and wurtzite structures are determined using an ab initio scheme. For the self-consistent-field part of the calculations, the Hartree - Fock program CRYSTAL has been used. Correlation contributions are evaluated using the coupled-cluster approach with single and double excitations. This is done by means of increments derived for localized bond orbitals and for pairs and triples of such bonds. At the Hartree - Fock level, it turns out that for SiC the zinc-blende structure is more stable although the very small energy difference from the wurtzite structure is an indication of the experimentally observed polytypism. For the III - V nitrides the wurtzite structure is found to be significantly more stable than the zinc-blende structure. Electron correlations do not change the Hartree - Fock ground-state structures, but energy differences are enlarged by up to 40%. While the Hartree - Fock lattice parameters agree well with experiment, the Hartree - Fock cohesive energies reach only 45% to 70% of the experimental values. Including electron correlations, we recover for all compounds about 92% of the experimental cohesive energies.