Ab-initio long-wavelenght properties of metallic systems : iron and magnesium

In this work we describe a method, based on the linearization of the band dispersion, to compute the intraband contributions to the optical spectra of metals. To investigate its performance we test it on cubic iron and hexagonal magnesium. We compute the dielectric function and optical conductivity of these metals based on ab initio DFT-LDA band structure, in the RPA with a full inclusion of local-field effects. In particular we show that our method is capable to describe the anisotropic response of noncubic metals, without the need to resort to phenomenological parameterizations of the plasmon-pole type. We also introduce a method to recover the correct asymptotic trend in the ω → 0 limit and hence, the experimental value of the static conductivity.