Calculating transition rates from durations of transition paths

Abstract

Calculating the kinetic rates for rare transitions is an important objective for molecular simulations. Here I prove equalities that relate the transition rates to the equilibrium free energy and the statistics of the transition paths. In particular, the durations of the transition paths within given intervals of the reaction coordinate provide the kinetic pre-factor in the rate formula. Based on the available free energy, the transition rates can further be rigorously calculated by initiating forward and backward simulations and evaluating the duration of each transition path. Validation on a model system confirms that the approach correctly predicts the transition rates from the simulations and demonstrates that whereas the relations here are general and valid for any chosen reaction coordinate, a good reaction coordinate will enable a more efficient sampling of the transition paths and thus a more reliable rate calculation.