Theoretical investigations of optical properties of FeF2

Density functional theory has been employed to determine ground state properties and calculate the complex dielectric function of the FeF2 compound. The complex expression of magnetic permeability has been estimated using the formula of the magnetic permeability tensor. To interpret the optical transitions, densities of states and projected densities of states have been determined. Suitable expressions for treating contributions of electric permittivity and magnetic permeability to optical properties have been derived and applied. The absorption coefficient in the visible range is a result of the transitions from the top of the valence band to 4s bands of Fe2+ cations in the conduction band. In the far-infrared region, FeF2 is a perfect reflector. The estimated optical properties show good agreement with previous theoretical and experimental results in the literature.