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 selfconsistent field part of the calculations, the Hartree-Fock program Crystal has been used. Correlation contributions are evaluated using the coupledcluster 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 zincblende structure is more stable although the very small energy difference to 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