Theoretical analysis of the momentum-dependent loss function of bulk Ag

We analyze the momentum-dependent loss function of bulk silver, calculated via the random-phase approximation and based on the band structure from semi-local density functional theory calculations. In the energy range of 0-55 eV the spectrum reveals the existence of seven well-pronounced peaks, in accordance with experiment. The two lowest of these are collective plasmon excitations, while the higher ones originate from inter-band transitions. Due to the different nature of those peaks, they display a different dependence on the momentum transfer q. While the plasmon peaks show an approximately quadratic q-dependence, the peaks caused by inter-band transitions are characterized by a much less pronounced dispersion. (C) 2009 Elsevier B.V. All rights reserved.