Ab initio intraband contributions to the optical properties of metals

We introduce a method, based on the linearization of the band dispersion, to include intraband contributions in ab initio calculations of the optical spectra of metals. We illustrate its application to cubic iron and hexagonal magnesium, by analyzing the contributions of interband and intraband transitions to the dielectric function and the optical conductivity. These calculations demonstrate a way to compute the conductivity anisotropy of noncubic metals without the need to resort to phenomenological parametrizations. In particular, we introduce a method to recover the correct asymptotic trend of the response functions in the omega -> 0 limit and hence compare directly with the experimental static conductivity.