Ab initio calculation of non-adiabatic couplings in condensed systems

Understanding and predicting chemical reactions in condensed phases, e.g. arising from photochemical and photophysical processes, remain challenging problems in physics and chemistry. A key question is how nuclear motion affects the electronic transitions involved in chemical reactions, i.e. understanding the non-adiabatic couplings (NACs) between nuclear and electronic states. These couplings govern non-radiative transitions, carrier recombination mechanisms, and internal-conversion (IC) processes. We developed an ab initio approach to compute the NACs in extended systems within the framework of Time- Dependent Density Functional Theory and present our results for the IC processes between electronic excited states in the negatively charged NV center in diamond, a promising platform for quantum technologies.