All electron, first principles, periodic calculations have been carried out
to investigate the relaxation of the Al-terminated corundum surface. Diffe
rent theoretical formalisms, Hartree-Fock (HF) and density functional theor
y using either the LDA or the hybrid B3LYP exchange-correlation functional,
have been employed. In the past, many ab initio studies of surface structu
re have been performed using the experimental, rather than the theoreticall
y optimized bulk structures. In the current study, we show that this leads
to significant differences in the predicted geometry. In addition, we demon
strate that optimizing a limited subset of surface parameters also has a si
gnificant effect on the accuracy of the final geometry. The extent of the e
ffect associated with each of these sources is shown to be strongly depende
nt on the choice of exchange-correlation potential. (C) 2001 Elsevier Scien
ce B.V. All rights reserved.