The interaction of Cu, Ag, and Au atoms with the regular terrace sites of the CeO 2 (111) surface has been investigated within the LDA+U and GGA+U density functional theory approaches using different U values and periodic slab surface models. For the interaction of Cu and Ag with this surface the different methods consistently predict the same qualitative description of stable active sites, the same order of stability and the oxidized character of adsorbed Cu and Ag. For the case of Au the description is more method dependent due to the nearly degeneracy between the solutions between cationic and neutral Au, in agreement with a recent study. The present results are indicative of the strength and limitations of the present density functional theory approaches.
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.
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