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 (ie, 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 …