It was discovered in calculation that jellium/slab model reduces the power of adsorbed atoms to attract the valence electrons. As a result

the computed minimum in work function-coverage curve by jellium/slab model is too low compared with the experiment

especially for Cs on Ir （001） system. In this paper

a jellium sphere/slab model is proposed. A star expanssion of charge density in jellium sphere-vacuum region is given. Finally

the examination on this model is carried out. The calculation shows that the effect of discrete charge distribution of adsorbed atoms gives a contribution about 0.4 eV and 0.8 eV to the work function for Cs on W（001） and Cs on Ir （001） system at the minimum respectively

which makes the computed values more closer to experimental ones.