Dynamic structure factors of Cu, Ag, and Au: A comparative study from first principles
We present a comparative theoretical and experimental study of dynamic structure factors (momentum-dependent loss functions) of the noble metals Cu, Ag, and Au in the energy range of 0$-$60 eV. The emphasis is on theoretical results that are compared with new as well as available experimental data. Dynamic structure factors are calculated within the linear-response formalism of time-dependent density-functional theory, using the full-potential linearized augmented plane-wave (FP-LAPW) method. For the studied energy range, local-field effects are found to be very important for Ag and Au and only marginally relevant for Cu. We present an explanation for this surprising behavior. Loss functions of all three metals possess a complex multi-peak structure. We classify the features in the loss function as being related to collective excitations, interband transitions, or mixed modes. The impact of short-range correlations on the dynamic response functions are evaluated by comparing the results of the random-phase approximation to those of the time-dependent local-density approximation. Exchange correlation effects are found to be weak for small momentum transfers, but increasingly important for larger momenta. The calculated structure factors agree well with experiments.