Ab initio calculations of the dynamical response of copper

The role of localized d bands in the dynamical response of Cu is investigated, on the basis of ab initio pseudopotential calculations. The density-response function is evaluated in both the random-phase approximation and a time-dependent local-density functional approximation. Our results indicate that in addition to providing a polarizable background which lowers the free-electron plasma frequency, d electrons are responsible, at higher energies and small momenta, for a double-peak structure in the dynamical structure factor. These results are in agreement with the experimentally determined optical response of copper. We also analyze the dependence of dynamical scattering cross sections on the momentum transfer.