New Simulation Method for Temperature Dependent Magnetic Circular Dichroism with Non-Perturbative Treatment of Magnetic Field

Magnetic circular dichroism (MCD) is an important experimental tool for probing open shell molecules, but the simulation is challenging. First, simulating MCD involves multiple perturbations, such as magnetic field, spin-orbit coupling and circularly polarized light. Second, the ground state Zeeman splitting comparable with kT makes MCD temperature dependent. Scientists used to parameterize temperature dependence, and evaluate the perturbation by sum over states or excited state gradient method. However, such perturbations increase the computational cost and fail in strong magnetic field. We developed a non-perturbative treatment of magnetic fields and spin-orbit coupling in linear response non-collinear TDDFT formalism, which simplifies the perturbation. It is especially advantageous for strong magnetic field. In order to resolve the temperature dependence of MCD, excitations are weighted by temperature dependent occupation number. This method is applied in Mo(CN)₈^3- and gives correct MCD-temperature dependence.