Passivated clusters: theoretical investigation of the effect of surface ligation on cluster geometry

A simple cluster ligand interaction model is introduced to describe the surface passivation of gold clusters by thiol ligands. It is shown that surface passivation effects can be considerable and can result in changes in the order of stability between different structural isomers. The fact that many empirical potentials favour icosahedral-based structures for bare metal clusters, while experimental studies show a preponderance of fcc-like cluster cores for passivated gold clusters, can be explained by a ligand-induced stabilisation of more open (100)-type surfaces in such clusters. These results are shown to be in agreement with more detailed calculations on specific cluster geometries.