Quantum dynamics in molecular systems: Theory and applications to intramolecular singlet fission

The accurate theoretical treatment and simulation of dynamical processes in many-body quantum systems is a long-standing goal in chemical and condensed matter physics. In this talk, I will discuss recent work in this field, focusing on time-dependent multiconfiguration methods. Formulated in the form of a tensor network, these variational basis-set methods facilitate accurate simulations of quantum dynamics in systems with many degrees of freedom. Applications of the methodology to photoinduced molecular processes are presented, including charge transport and singlet fission, a multiple exciton generation process in molecular materials. Considering specifically intramolecular singlet fission in pentacene dimers with different linker groups, the mechanisms of this photophysical process are analyzed, in particular the role of the involved electronic states and the effect of electronic-vibrational coupling. It is shown that the formation of the multiexciton state, corresponding to the first step of the singlet fission process, occurs mainly through a superexchange-like mechanism involving charge transfer states and is facilitated by vibronic coupling.