Natural optical activity in solids from Wannier interpolation

Optical responses of materials are described by the optical conductivity, which, in the presence of spatial dispersion, depends on the wave vector q of incident light. The first-order term in q, which is present when inversion symmetry is broken, describes natural optical activity and related phenomena such as optical rotation (OR), circular dichroism (CD), and magneto-optical effects. In this talk, we present an implementation of the calculation of the spatial-dispersive optical conductivity via a Kubo formulation, using Wannier interpolation. This technique is particularly well suited for treating interband optical transitions in small-gap semiconductors because these require a fine sampling in reciprocal space to obtain a well resolved spectrum, a requirement that is hard to meet with direct ab initio calculations. We test our implementation by computing the CD of GaN and the OR of trigonal Te, comparing our results to those obtained in previous literature. We also compute the OR of trigonal Se and discuss our results in light of the substantial effect of local fields recently addressed from a density functional perturbation theory standpoint.