Density-Functional Theory Approach to Thiols and Disulfides on Gold: Au(111) Surface and Clusters

We discuss our recent ab initio calculations of the adsorption configurations (both dissociative and not) of methanethiol and dimethyl disulfide on Au(111) at low coverage, which are based on density- functional theory using gradient-corrected exchange-correlation functionals (both BLYP and PBE). A complete characterization of their structure, binding energies, and type of bonding is obtained. Dissociation is clearly favored for the disulfide with subsequent formation of strongly bound thiolates, in agreement with experimental evidence, whereas thiolates resulting from S-H bond cleavage in thiols can coexist with the adsorbed "intact'' species and become favored if accompanied by the formation of molecular hydrogen. New calculations are also presented for the thiolates and the disulfide on a 38-atom gold cluster. Differences and similarities of the bonding on the cluster and on the surface are described in detail.