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

The structure of the α-Al2O3(0001) surface has been the subject of a number of investigations which have yielded results that are both qualitatively and quantitatively different. Previous theoretical studies differ both in terms of the numerical approximations employed and the underlying treatment of electronic exchange and correlation. We have re-examined the surface structure using a variety of exchange–correlation functionals within the same numerical scheme. We find a suprisingly large variation in the predicted surface structure with the choice of functional. The computed geometries are consistent with all previous theoretical predictions and we have thus managed to unify these apparently disparate results. Nevertheless, the predicted structure is at variance with that deduced from experimental studies, particularly with respect to the contraction of the first-to-second interlayer distance. Possible reasons for this discrepancy are discussed.