Modification of transition metal electronic structure by P, S, Cl, and Li adatoms

Abstract

We have evaluated the electronic perturbations induced on a thin Rh(001) film by the adsorption of 1/4 monolayer coverages of P, S, Cl or Li atoms. The self-consistent Surface Linearized Augmented Plane Wave (SLAPW) calculations indicate that the P, S, and Cl adlayers cause only very slight work function changes, and generally give rise to perturbations in the valence charge that are small beyond the nearest neighbor Rh atoms. We attribute the latter result to the effectiveness with which the charge density is screened. In contrast, reductions induced in the Fermi level Local Density of States (Ef-LDOS), whose magnitude reflects the ability of the surface to respond to the presence of reactants, are substantial even above next nearest neighbor Rh atoms, which are 8 a.u. away. The effect is strongest for Cl and weakest for P. When Li is adsorbed, the work function is reduced by almost 2 eV. This decrease is associated with an increase in electronic charge density over most of the surface, and at the same time, an increase in the Ef-LDOS. Experimental observations of CO adsorption and dissociation on transition metal surfaces indicate a “poisoning” effect by coadsorbed P, S, and Cl atoms and a “promotion” effect by coadsorbed alkali atoms. The SLAPW results for the Ef-LDOS parallel these observations.