The density functional theory was used to examine the electronic structure of small Au clusters, supported on rutile TiO2(110) surfaces having subsurface Ti-interstitials. The interstitials reduce the surface and it was found that  negatively charged gold clusters were stabilized with respect to the stoichiometric surface. The behaviour of the open-shell gold clusters could be rationalized in terms of the highest occupied molecular orbitals and the resulting electron affinities. The relative stabilities of closed-shell gold clusters led to recent disagreements in the literature. It was shown that they were very dependent on the density functional used. As expected, a red-shift in the CO stretch vibration was calculated for CO adsorbed on a negatively charged cluster. Somewhat surprisingly a larger red-shift was found for CO adsorbed on an overall positively charged Au3 cluster. This was explained by CO being a local probe of the individual Au charges and one Au atom having an electron accumulation.

Effect of Subsurface Ti-Interstitials on the Bonding of Small Gold Clusters on Rutile TiO2(110). Madsen, G.K.H., Hammer, B.: Journal of Chemical Physics, 2009, 130[4], 044704