Density functional study of the structural and electronic properties of RuS2(111) I.: Bare surfaces

Trends in the surface relaxation and electronic properties of RuS2(111) as a function of the sulfur concentration at the surface have been investigated by ab initio density functional calculations. Consistent with experimental and previous theoretical studies, sulfur-enriched terminations without exposed unsaturated metal atoms (anionic vacancies) turn out to be more stable compared to the stoichiometric and highly reduced surfaces. Terminations invoking the simultaneous occurrence of a full S-2 perpendicular-pair and a single S-atom from a broken tilted pair are not energetically favored, as predicted by the calculated formation enthalpies. The observed S-Ru bond strengthening at the surface for terminations with anionic vacancies is related to the increased hybridization between sulfur 3p-pi and ruthenium 4d bands. (C) 1999 Elsevier Science B.V. All rights reserved.