First-principles optical response of semiconductors and oxide materials

The calculation of the optical gaps of a series of nonmagnetic direct and indirect semiconductors and simple oxides is addressed using an all-electron perturbative method based on density-functional theory. Hybrid exchange, in both the Kohn-Sham spectrum and the perturbative response, is shown to be essential to achieve an accuracy comparable to experimental estimates for all systems studied, including those exhibiting excitonic transitions at the absorption edge. In agreement with existing evidence it is shown that a proper description of excitonic features relies crucially on the nonlocality of the response equations.