Local-field effects on the optical properties of non-cubic crystals

A method is developed that allows effective calculation of local-field effects on optical properties of non-cubic crystals in the Random Phase Approximation, expanding electron wave-functions on localized orbitals. Adler and Wiser's formula of the macroscopic dielectric constant is generalized to the case of non-cubic crystals, where a macroscopic dielectric tensor is defined in terms of Wannier functions.