Optical Properties of Materials Calculated from First Principles Theory

Abstract: In this project work, we performed ab-inito calculations for 20 different non-magnetic materials (band gap ranging between 0.5 eV to 13 eV ) and three different magnetic materials such as NiO, EuO and GdN using density functional theory (DFT). Generalized gradient approximation (PBE) and hybrid functional (HSE06, PBE0) within projector-augmented wave (PAW) methodology were adopted to investigate the electronic properties, whereas only PBE approximation was used to study optical properties of these materials. Furthermore, for magnetic materials, PBE+U method was employed to treat the strongly correlated d and f electrons. Subtle difference in f electron state at the Fermi level in EuO and GdN for different approximations was thoroughly evaluated here. Using HSE06 we have showed that for non-magnetic materials the band-gap values were comparable with the experimental values. ForEuO we have observed a band-gap of 0.8 eV by using PBE+U approximation. However, in the HSE06 approximation, no band-gap was observed at Fermi level. The optical properties for non-magnetic systems were evaluated by calculating the dynamic dielectric functions such as absorption, reflection and energy-loss spectroscopy with the help of self-developed numerical codes. The static dielectric matrices of materials were calculated using density functional perturbation theory. The static dielectric constant values were calculated by different approaches: i) by including local field effects in both DFT and random phase approximations (RPA) and ii) excluding local field effects and including local field effects in DFT. The static constant values of the materials including local field effects for RPA approximation yielded better results than other methods.