A correlated ab initio treatment of the zinc-blende wurtzite polytypism of SIC and III-V nitrides

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-held 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.