Ab initio calculations are used to study the reduction of the work functions of tungsten (W) surfaces with 1 ML of adsorbed barium (Ba) and lithium atoms. The authors carefully and systematically tested the convergence of density-functional-theory (DFT) calculations in the local-density approximation orgeneralized-gradient approximation with a plane-wave basis set and ultrasoft pseudopotentials or the projector-augmented wave method as implemented in the Vienna ab-initio simulation package. The DFT calculation shows that the work function of the Ba adsorbed onto a p (2x2) 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. (c) 2008 American Vacuum Society.