Ultrafast Nonadiabatic Dynamics of Singlet Fission: Quantum Dynamics with the Multilayer Multiconfigurational Time-Dependent Hartree (ML-MCTDH) Method

Singlet fission (SF) is supposed to potentially improve the efficiency of solar energy conversion in organic photovoltaic systems. The multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method was employed to describe the singlet fission of the pentacene system with a three-state model. The ML-MCTDH result agrees well with the previous simulations using the Redfield theory, the hierarchical equation of motion (HEOM) and the symmetrical quasi-classical (SQC) theory. We carefully investigated the role of vibrational modes with different frequencies in singlet fission dynamics. Interestingly, we observed the important contribution of a few modes with frequency resonance to electronic transition. Such a finding can be understood by revisiting the superexchange mechanism within the framework of Fermis golden rule. As a numerically exact method, ML-MCTDH not only provides an accurate description of the microscopy insight of the SF dynamics but also provides benchmark results to examine the performance of other approximated dynamical methods.