Prediction of a Ag multipole surface plasmon

It is argued that Ag should exhibit a multipole surface plasmon near ωₘ≈0.8ωₚ≈7 eV (ωₚ≈9 eV is the s-electron bulk plasma frequency) since the density profile at the surface has predominantly s-electron character and since the multipole mode is much less affected by s-d screening than the monopole surface plasmon. Calculations of nonlocal optical spectra based on the s-d polarization model and the time-dependent density-functional approach support this picture.