Electronic structure and relative permittivity of α-alumina in the generalized gradient approximation
Pristine α-alumina or α-Al2O3 is a wide band gap insulator with notable hardness and clarity that make it a prime material for a range of optical and commercial applications. We present first principles calculations of the electronic and optical properties of α-alumina in the generalized gradient approximation. While our results match those of other studies using similar approximations, these computations yield systematically smaller band gaps than observed in experiments. Consequently, the predicted absorption spectrum is redshifted and the refractive index is overestimated. This study serves as a benchmark for future work involving more sophisticated hybrid exchange-correlation functionals that are needed to accurately describe how dilute substitutional defects can form narrow transmission bands in the visible spectrum.