DYNAMICAL EFFECTS IN THE CALCULATION OF QUANTUM RATES FOR ELECTRON-TRANSFER REACTIONS

This paper presents results of path-integral quantum dynamics simulati ons of electron transfer rates in a simple class of model Hamiltonians for symmetric and asymmetric electron transfer systems. Our study is aimed at testing the practical usefulness of a centroid factorization of the electron transfer rate constant in the deep tunneling regime. T o circumvent the sign problem in quantum Monte Carlo simulations of th e electron flux, local filtering techniques have been employed. The si mulations show that due to dynamical effects, the reactive flux far ou tside the transition state region also plays an important role in dete rmining the rate. These results suggest that while the centroid formul ation of the equilibrium (imaginary-time) quantum transition state the ory (QTST) applied to the electron path is accurate for nonadiabatic e lectron transfer reactions, dynamical (real-time) effects can produce significant corrections to the QTST estimate for the rate outside this region. For model parameters characteristic for a chemical electron t ransfer system, we found that the rate is enhanced by a factor Z(e) al most-equal-to 4. The origin of these dynamical corrections can be unde rstood within a perturbation theory in the number of kinks on the imag inary-time electron quantum path.