Work Function of Transition-Metal Surface with Submonolayer Alkali-Metal Coverage

The film linearized-augmented-plane-wave method with a refined set of basis functions in the jellium-vacuum region is used to calculate the electronic structure of a model system simulating a W(100) surface covered by a Cs overlayer from zero to monolayer coverage. The work function decreases rapidly with coverage at the initial stage of adsorption, reaches a minimum at $\theta =0.22\mathrm{}$, and rises again at higher coverage, in good agreement with experiment. The changes of the electron distribution and potential reveal that the initial decrease of the work function is caused by electron transfer from the Cs to the W surface.