Density-functional-theory calculations of the optical properties of Al2O3: From solid-state to warm dense matter conditions

Abstract

Aluminium oxide (Al2O3) in extreme conditions is present in many high energy density (HED) experiments, as well as in disintegrating extra-solar planets (exoplanets). Understanding the changes in the optical properties of Al2O3 in conditions of extreme temperatures is necessary for designing HED experiments, and the interpretation of astronomical observations. However, there are no calculations of the optical properties of HED Al2O3 in the literature. Here, we present density functional theory (DFT) calculations of the optical properties of Al2O3 for photon energies from 0 to 90 eV in conditions ranging from crystalline to warm dense matter conditions, at solid densities. Changes of the optical properties due to increasing temperature are explained in terms of the changing electronic structure and electron occupation. To benchmark the DFT approach adopted here, the calculations are compared to available experimental data of cold solid Al2O3 from other studies.