The electronic structure and oxidation state of atomic Au adsorbed on a perfect CeO(2)(111) surface have been investigated in detail by means of periodic density functional theory-based calculations, using the LDA+U and GGA+U potentials for a broad range of U values, complemented with calculations employing the HSE06 hybrid functional. In addition, the effects of the lattice parameter a(0) and of the starting point for the geometry optimization have also been analyzed. From the present results we suggest that the oxidation state of single Au atoms on CeO(2)(111) predicted by LDA+U, GGA+U, and HSE06 density functional calculations is not conclusive and that the final picture strongly depends on the method chosen and on the construction of the surface model. In some cases we have been able to locate two well-defined states which are close in energy but with very different electronic structure and local geometries, one with Au fully oxidized and one with neutral Au. The energy difference between the two states is typically within the limits of the accuracy of the present exchange-correlation potentials, and therefore, a clear lowest-energy state cannot be identified. These results suggest the possibility of a dynamic distribution of Au(0) and Au(+) atomic species at the regular sites of the CeO(2)(111) surface.

Periodic density functional calculations within the LDA+U and GGA+U formalisms have been carried for slabs representing the CeO2(111) surface and a stepped model surface. The surface active sites have been determined and the chemical bond between Au and the underlying substrate quantified by means of analysis of Bader charges and calculated magnetic moments. For most of the active sites involving O atoms at (111) terraces or at the corresponding step edges the adsorption energy is very similar (∼0.7 eV), and adsorbed Au remains essentially neutral. However, the interaction of Au with one of the facets intersecting the (111) terrace is much stronger (2.4 eV), and the adsorbed metal atom is oxidized. The present results permit one to understand the very large effect of nanostructured ceria on the activity of Au supported catalysts reported recently.