Surface strain effects on the adsorption and the diffusion of Au atoms on MgO(001) surfaces

The effects of surface strain on the adsorption and the diffusion properties of a Au adatom on MgO(001) surfaces are studied using first-principles electronic-structure calculations based on the density functional theory. The adsorption of Au on MgO(001) is found to become stronger with increasing surface strain. In addition, the adsorption site of Au changes from a site on top of a surface O atom of MgO(001) to a site near a surface O atom for tensile surface strains over +4 %. In the case of a tensile surface strain of +7 %, the adsorption energy changes from -0.87 eV for unstrained MgO(001) to -1.17 eV. The variation in the charge states of Au on MgO(001) with surface strain, based on a Bader charge analysis, is also presented. The Bader charges of Au are found to become more negative as the surface strain increases. For a tensile surface strain of +7 %, the Bader charge is -0.38 |e|, more negative than the value of -0.29 |e| for unstrained MgO(001). Contrary to the adsorption energies and the charge states of Au, the variation in the surface diffusion barriers of Au on MgO(001) is found to be very small, less than 0.03 eV.