Ab initio Predictions of Circular Dichroism in Chiral Crystals

Chirality in materials is of increasing recent interest especially because of its strong coupling to spin dynamics, such as in the Chirality-Induced Spin Selectivity effect. Designing new chiral materials and benchmarking their optoelectronic properties, including circular dichroism (CD) and optical rotation, is therefore of increasing importance. Here, we present a framework for first-principles prediction of CD of chiral crystals starting from the independent particle approximation and identify key conceptual and computational extensions necessary beyond the well-established theory of CD in molecules. Specifically, we show that CD in general anisotropic crystals is a rank-2 tensor in terms of the wave propagation direction, and requires treatment of electric quadrupole matrix elements in addition to magnetic dipole ones. We validate our framework with excellent agreement with experimental measurements on molecular benchmarks, as well as crystals ranging in complexity from elemental chiral semiconductors, such as tellurium and selenium, to hybrid halide perovskites. Finally, we show that the impact of spin-orbit coupling on the CD of crystals with heavy elements is primarily due to changes in the electronic energies, rather than through spin matrix element contributions.