Charging of atoms, clusters, and molecules on metal-supported oxides: A general and long-ranged phenomenon

The density-functional theory is used to investigate the adsorption of Au atoms, Au clusters, and NO₂ molecules on transition-metal-supported oxides. As compared to unsupported oxides, the adsorbates on supported oxide films are charged and experience a higher adsorption energy. The origin of the effect is explored by considering two different oxides (MgO and Al₂O₃) and a range of supporting metals. Moreover, the limits of the enhancement are probed by explicit calculations for thick MgO films and low coverage. The long-range character of the phenomenon is attributed to electrostatic polarization. The absolute strength depends on several contributions and their relative importance changes with system composition.