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

TL;DR

This study uses ab initio methods to compare the stability of zinc-blende and wurtzite structures in SiC and III-V nitrides, revealing how electron correlations influence their relative energies and cohesive properties.

Contribution

It provides a detailed ab initio analysis of polytypism in SiC and nitrides, incorporating correlation effects with coupled-cluster methods to improve energy predictions.

Findings

Zinc-blende is more stable for SiC at Hartree-Fock level.

Wurtzite is more stable for III-V nitrides.

Electron correlations increase energy differences by up to 40%.

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. A comparison between the ground state energies of the zinc-blende and wurtzite structure is made: At the Hartree-Fock level, it turns out that for SiC the zinc-blende 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 compounds about 92% of the experimental cohesive energies.