Calculation of the electronic work function of Cu and Ag from an extended jellium model

We propose an extended jellium model which includes the most important features of the noble metals. The density of states is modeled by the superposition of a d band and an s-like conduction band. The redistribution of some of the d electrons into the conduction band as an effect of the s-d hybridization is taken into account, and the conduction band includes 1.5 electrons per atom. We show that the occupation number $Z_d$ of the d band is mainly determined by the ratio $W_d$/(${\varepsilon }_F$-${\varepsilon }_d$), where $W_d$, ${\varepsilon }_d$, and ${\varepsilon }_F$ are, respectively, the width and the center of the d band and the energy of the Fermi level. The shift of the d-band center between the bulk metal and the surface plane is related to the narrowing of the d band of the surface plane, and we deduce an estimate of the d-band contribution to the work function. In the present model the position of the Fermi level and of the d-band center are reproduced, and the result for the work function of Cu and Ag is satisfactory.