Origin of positive core-level shifts in Au clusters on oxides

The origin of observed positive core-level shifts in sparse Au clusters on oxides is explored in representative metal oxide systems, namely, Au/MgO(001) and Au/TiO₂(110) with a varying coverage and also in the presence of surface oxygen vacancies, by using the density-functional full-potential-linearized augmented-plane-wave method. The final-state effects are treated self-consistently by moving one core electron to the valence band. This approach provides excellent results for binding energies. Surprisingly, it is not the final-state contribution but the presence of surface O vacancies that causes the positive core-level shifts.