Gold and Silver Custers on TiO2 and ZrO2 (101) Surfaces: Role of Dispersion Forces

The adsorption of Ag and Au atoms and Ag4 and Au4 clusters on the stoichiometric TiO2 (anatase) and ZrO2 (tetragonal) (101) surfaces has been investigated using DFT+U calculations with and without the inclusion of van der Waals (vdW) forces. We considered the effects of vdW interactions on the physical properties of the adsorbed species using three different approaches: two variants of the pairwise force field method proposed by Grimme (DFT+D2 and DFT+D2′), and the vdW-DF method in which the vdW contribution is expressed directly as a function of the electron density. The results show that, already at the level of metal atoms and small clusters, the inclusion of vdW interactions can change the order of stability of various isomers and, more importantly, can result in major corrections to the adsorption energies. These effects can, in turn, affect other properties such as the structure and chemical reactivity of supported metal particles on oxides or their diffusion properties.