Optical properties of calcium under pressure from first-principles calculations

Abstract

Here we present theoretical ab initio calculations based on time-dependent density-functional theory of the macroscopic dielectric function of calcium from 0 to 110 GPa in the fcc, bcc, and sc phases. All the dielectric functions are calculated using very fine reciprocal space meshes since both eigenvalues and matrix elements entering in the density-response functions are interpolated using Wannier functions. Our calculations correctly predict the energies of the low- and high-energy plasmons observed in the fcc phase at room pressure. Moreover, we predict that in the sc phase a very low-energy interband plasmon emerges at around 50 GPa that dramatically modifies the behavior of the reflectivity making it almost vanish at the plasmon energy. As a consequence, calcium becomes an example of how optical properties can become complex under pressure.