Influence of d electrons on the dispersion relation of Ag surface plasmonsfor different single-crystal faces - art. no. 165407

The surface plasmon dispersion relation of Ag is calculated for different s ingle-crystal orientations. To describe the dynamical response properties o f both delocalized 5s electrons and more tightly bound 4d electrons, the je llium model is combined with the so-called dipolium model, in which the occ upied Ag d bands are represented in terms of polarizable spheres located at the sites of a semi-infinite fee lattice. The nonlocal susceptibility char acterizing the s electron response in the surface region is derived using d ensity functional theory. The screening of the Coulomb interaction between conduction electrons via the lattice of dipoles, and of the dipole interact ion via the surrounding sea of conduction electrons, is treated self-consis tently. Electron energy loss spectra are calculated for all three low-index faces. The surface plasmon energy is found to increase with parallel wave vector for all cases. The magnitude of the positive slope depends on the cr ystal orientation and, for Ag(110), on the propagation direction. These res ults are in qualitative agreement with electron energy loss measurements.