Electronic structure methods for the investigation of nonadiabatic dynamics

A detailed understanding of the interface between nuclear dynamics and electronic structure is crucial for describing excited state dynamics in photoexcited systems, a key aspect of modelling the efficiency of photovoltaic devices, among other applications. There has been a proliferation of techniques for approaching the problem of electronic-nuclear interactions from the perspective of both electronic structure and nuclear dynamics; the work presented here focuses on the electronic part of the equation. Methods are developed for alternative electronic representations, called diabatic representations, that anticipate the effects of nuclear momentum and attempt to minimize them. Diabatic representations can also be used to describe the electronic states involved in charge transfer or energy transfer processes, providing couplings necessary for approximating rates using Marcus theory. In addition, analytic techniques are developed that measure the impact of nuclear motion on electronic states, which can be used in the context of a dynamics simulation to approximate rates of energy transfer, charge transfer, or other types of internal conversion in chemical systems for which Marcus theory is insufficient. These methods are then used to couplings and rates for triplet-triplet energy transfer and singlet fission systems