How to calculate the rate constants for nonradiative transitions between the <i>M_S</i> 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 mechanisms many photochemical and catalytic reactions. To calculate these rates, it necessary to define state representation couplings that drives interstate transitions. In this work, we describe three approaches calculating spin–orbit coupling (SOC), transition probabilities, rate constants MS components multiplicities. We implemented in our nonadiabatic statistical theory (NAST) software package, which predicts probabilities using information obtained from structure calculations. discuss advantage drawbacks each approach and, as an example, active site model protein rubredoxin.