How to calculate the rate constants for nonradiative transitions between the MS components of spin multiplets?

Predicting the rates of spin-dependent processes characterised by nonradiative transitions between electronic states with different spin multiplicities is important for understanding the mechanisms of many photochemical and catalytic reactions. To calculate these rates, it is necessary to define the spin state representation and the couplings between these states that drives the interstate transitions. In this work, we describe three different approaches to calculating the spin-orbit coupling (SOC), transition probabilities, and rate constants between the M-S components of the electronic states with different spin multiplicities. We implemented these approaches in our nonadiabatic statistical theory (NAST) software package, which predicts the transition probabilities and rate constants of spin-dependent processes using information obtained from electronic structure calculations. We discuss the advantage and drawbacks of each approach and, as an example, calculate the rate constants for transitions between the spin states in the active site model of the protein rubredoxin.

Automated summary

Predicting the rates of spin-dependent processes characterized by nonradiative transitions between electronic states with different spin multiplicities is crucial for understanding the mechanisms of photochemical and catalytic reactions. This study introduces three different approaches to calculate the spin-orbit coupling, transition probabilities, and rate constants between electronic states with different spin multiplicities. These approaches are implemented in the NAST software package, which predicts transition probabilities and rate constants using information from electronic structure calculations. The rates of transitions between spin states in the active site model of rubredoxin are calculated as an example.