The effect of electric fields on Ag(001) c(2x2)-Xe

The electronic structure of Ag(001) with an adsorbed overlayer of Xe is calculated in external electric fields of varying strength. The screening mostly takes place on the top of the surface Ag atoms, with polarization of the Xe atom. The variation in the centroid of the screening charge (the image plane) with field strength is studied, and it is found that the adsorption of Xe reduces the non-linear response compared with that of the clean Ag surface. The distribution of screening charge between the various atoms is found using a generalized effective charge, and it is found that the screening charge on Ag atoms directly underneath Xe is enhanced. The generalized effective charge gives the derivative of the force at the surface with respect to the electric field, and the phenomena of field-induced chemisorption and field desorption are discussed in these terms.