First-principles study of adsorption, diffusion, and charge stability of metal adatoms on alkali halide surfaces

In this work we have performed first-principles calculations based on the spin-polarized density-functional theory for the adsorption and diffusion of Au, Ag, and Pb atoms on NaCl(001), KCl(001), and KBr(001) surfaces. We consider also the influence of adatom charge on the adsorption and diffusion. In order to characterize the different systems we explicitly calculate charge transfer between surface and adatom and consider the relative stability of the various charge states. Our results show that in general, apart from positively charged systems, the adatoms are weakly bound to the surface via orbital polarization and ionic interactions, and relatively little charge transfer occurs. Au and Ag adatoms are highly mobile on all surfaces, although they can be pinned by removal of an electron. In contrast, Pb adatoms are fairly immobile, and their mobility increases upon charging. Analysis of the charge stability suggests that Ag offers the potential of charge controlled mobility on insulators.