Theoretical Investigation of the Deposition of Cu, Ag, and Au Atoms on the ZrO₂(111) Surface

We have used computer modeling techniques to investigate the interaction of Cu, Ag, and Au atoms (at 0.25 ML coverage) with the (111) surface of zirconia, ZrO 2 . The surface was simulated by means of periodic slabs, and the calculations were performed using spin-polarized density functional theory (DFT) within the generalized gradient approach. We show that, for the three metals, the most stable adsorption sites are not on top of the outmost oxygen atoms, as previously suggested for the Cu/ZrO 2 case, but at less-symmetric bridge sites between oxygen and zirconium. Furthermore, the examination of the charge density and the electronic density of states shows that no full charge transfer takes place between any of the metals and the zirconia surface, as, in all cases, the metal's unpaired electron remains largely localized on the metal adatom upon adsorption. The origin of the interaction appears to be the polarization of the electronic density of the adsorbed metal atom, together with a modest chemical contribution arising from the mixing of the orbitals of the metal atom and the surface oxygen. The adsorption energies follow the order | E ads (Ag)| < | E ads (Au)| < | E ads (Cu)|.