Self-energy of an electron in a gap between two metals and near a metallic slab

Using the formalism of Manson and Ritchie, we have calculated the self-energy of an electron located in the gap between two similar metals and near a metallic slab. The electron is described in terms of a plane-wave basis set. Numerical work indicates that for gap separations {}4 A{}, quantal corrections to the classical image potential are not large in the case of a zero-momentum electron.