Interaction, electron transfer, and work function of a chemisorbed alkali-metal submonolayer on a W(001) surface

The linearized-augmented-plane-wave method is applied to the submonolayer alkali-metal chemisorption on a transition-metal W(001) surface. The adsorbate-substrate system is described by the jellium-slab model. Several jellium thicknesses are used to simulate different adsorbates. The dependences of the work function on the coverage and the jellium thickness are in good agreement with experiment. It is found, moreover, that the interaction of the adlayer and the substrate are ionic when the coverage is less than 0.18\ifmmode\times\else\texttimes\fi{}${10}^{15}$/${\mathrm{cm}}^{2}$ for all alkali-metal surface state of W(001). At higher coverage, a polarized metalliclike interaction is gradually formed due to the hybridizing of this surface state with the s-like state of the alkali-metal adatom. The hybridized state in the interface is lowered in energy by 2.6--1.0 eV with respect to different adsorbates from Li to Cs.