Effect of the surface states of different transition-metal substrates on a Cs overlayer

The linear augmented-plane-wave method is applied within the jellium-slab model to investigate the submonolayer cesiated (001) surfaces of Ta, W, Ir, Pt, Au, Ni, and Cu. At lower coverages, it is an ionic-adsorption regime in which the alkali-metal adlayer donates its electrons to the most influential surface state of the substrate. The characteristic coverage ${\mathit{N}}_{\mathit{m}}$, which marks the end of the ionic adsorption and is a measure of the ability of the most influential surface band of the substrate to hold extra electrons, decreases with increasing number of d electrons in the substrate atom. At higher coverages, however, the dipole moment p of the adsorption layer decreases rapidly, and in this polarized-metallic regime adsorption electrons are depolarized mainly by the Coulombic effect within the adlayer. The work-function minimum (0.5 eV) and the work function at the monolayer coverage (1.8 eV) are independent of the choice of substrate.