Dramatic lowering of work function for the barium atoms adsorbed onto a p(2x2) W(001) substrate based on Ab initio calculations

Ab initio calculations are used to study the reduction of the work functions of tungsten (W) surfaces with one monolayer of adsorbed barium (Ba) and lithium atoms. We have carefully and systematically test the convergence of density-functional-theory (DFT) calculations in the local-density approximation or generalized-gradient approximation with a plane-wave basis set and ultra-soft pseudopotentials or the projector-augmented wave method as implemented in Vienna ab-initio simulation package. The DFT calculation shows that the work function of the Ba adsorbed onto a p(2times2) W(001) substrate is dramatically lowered by about 2.2 eV, provided that the fourfold hollow sites are occupied. With this approach, one can investigate more complex adsorbates onto the cathode surface of different materials.