An ab initio study of alpha-Al2O3(0001): the effects of exchange and correlation functionals

The structure of the alpha-Al2O3(0001) surface has been the subject of a nu mber of investigations which have yielded results that are both qualitative ly and quantitatively different. Previous theoretical studies differ both i n terms of the numerical approximations employed and the underlying treatme nt of electronic exchange and correlation. We have re-examined the surface structure using a variety of exchange-correlation functionals within the sa me numerical scheme. We find a suprisingly large variation in the predicted surface structure with the choice of functional. The computed geometries a re consistent with all previous theoretical predictions and we have thus ma naged to unify these apparently disparate results. Nevertheless, the predic ted structure is at variance with that deduced from experimental studies, p articularly with respect to the contraction of the first-to-second interlay er distance. Possible reasons for this discrepancy are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.