Rapid calculation of internal conversion and intersystem crossing rate for organic materials discovery

The internal conversion (IC) process from S1 to S0 and the intersystem crossing (ISC) transition from T1 to S0 are two essential processes in functional molecular material design. Despite their importance, it is currently impossible to evaluate the rate of these processes for a large set of molecules and, therefore, perform high-throughput virtual screening in large-scale data to gain more physical insight. In this work, we explore possible approaches to accelerate the calculations of IC and ISC rates based on a systematic reduction of the number of modes included in the computation and the study of the importance of the different parameters and the influence of their accuracy on the final result. The results reproduce the experimental trends with systematic errors that are ultimately due to the approximations of the theory. We noted that plausible results for ISC in planar molecules are only obtained by including the effect of Hertzberg-Teller coupling. Our method establishes the feasibility and expected accuracy of the computation of nonradiative rates in the virtual screening of molecular materials.