Wavenumber dependence of the energy loss function of graphite and aluminium

The energy loss function of a material is a key parameter in the dielectric formalism used to describe the optical spectra and the excitations produced by swift charges in solids. Modelling the experimental energy loss function as a sum of Mermin type functions in the optical limit (i.e., at zero momentum transfer), we have calculated its dependence on the momentum transfer. We compare the result with available experimental data for graphite and aluminium and with other theoretical models. We find a reasonably good agreement of our results with these data, and better agreement than is obtained with other models.