Sulphur overlayers on lr and its effect on the adsorption of CO: a DFT study

Ordered sulphur overlayers adsorbed on Ir(100) surface are studied with different coverage ranging from 0.11 to 1.0 ML. Calculations indicate that atomic S adsorbs favourably in hollow sites, forming strong covalent bonds with the substrate surface and the adsorption energy is nearly unchanged at lower coverages ([θ.sub.S] ≤ 0.50 ML). In good agreement with experimental observations, the p(2 x 2)-S and c(2 x 2)-S are predicted to be the most stable overlayers. The obtained surface electronic structure modifications induced by sulphur adsorption are coverage-dependent and the results are in accordance with the rectangular band and the Hammer-Norskov models. Moreover, the effect of sulphur on the adsorption of CO is discussed in the p(2 x 2)-(S+CO) overlayer on Ir(100).