First-principles study of the adsorption of sulfur on Pt(111): S core-level shifts and the nature of the Pt-S bond

The adsorption of a sulfur atom and a sulfur molecule on the Pt(111) surface is investigated through the first-principles full-potential linearized augmented plane-wave (FLAPW) and pseudopotential calculations. Different sulfur coverages (0.25, 0.33, and 1 ML) and several adsorption geometries are considered. It is found that, for atomic sulfur, the S-Pt bond is weakened with the increase of sulfur coverage and the most stable adsorption site changes from fcc-hollow site to atop site. The S 2p core levels shift to higher binding energy with the increase of S coverage. The Pt 4f core levels are stabilized upon interaction with the S adsorbate, and yet the Pt to S charge transfer is not substantial in many cases. S adsorption induces significant decreases in the density of Pt 5d states near the Fermi energy. For the case of S-2 adsorption, the S-S bond length is 2.1 Angstrom with one atom near an atop position and the other on a mixed bridge-hollow site. The adsorption energy is close to 44 kcal/mol.