Studies of adsorption of alkali atoms on A1(111) as a function of coverage

We have studied the adsorption of alkali atoms on Al(111) for different coverages θ. We calculate the total energy of the system in which the ionic interaction potential is described by pseudopotentials averaged over the parallel directions to the surface. This method allows us to consider all regimes in θ. We find that adsorbed alkali atoms evolve from ionic to metallic and from low to large coverages. In particular, we calculate for the Cs/Al(111) system that the equilibrium distance increases 0.12 Å when coverage changes from 0.4 to 1 ML. Work functions are also presented. We note that in order to obtain well-defined values of the distance, it is necessary to keep the substrate at a low temperature, because the energy minima are very shallow as a function of the adatom-substrate separation. © 1991.