Evolution of atomic and electronic structures of Cu-n (n=2-10) clusters supported on anatase TiO2(101) surface

Based on extensive structural search and density functional theory (DFT) calculations, the atomic and electronic structures of of Cu-n (n = 2-10) clusters supported on anatase TiO2(1 0 1) surface (denoted as Cu-n/A(1 0 1)) are systematically studied. The atomic structures exhibit obvious hereditary feature, i.e. most of the low-energy structures of larger clusters can be obtained by adding additional Cu atoms onto those of smaller clusters. Small sized clusters (n <= 6) prefer to quasi planar structures while large sized clusters (n > 6) prefer to complex three-dimensional structures. The thermodynamic stabilities of the supported Cu-n clusters are investigated by calculating the binding energies, second order energy difference, adsorption energies and nucleation energies. It is found that Cu-3/A(1 0 1), Cu-5/A(1 0 1), and Cu-8/A(1 0 1) are particularly stable and Cu-3, Cu-5 and Cu-9 clusters would be stabilized by the substrate mostly. All these Cu-n clusters can introduce in-gap states and reduce the band gaps according to the calculated density of states. Supported Cu-n clusters play the role of electron donor, resulting in partial oxidation state Cu5+ and zero valence state Cu-0.