Computational methods for electron-transfer systems

Electron-transfer processes, and especially light-induced electron-transfer reactions, play an extremely important role in natural and artificial energy transduction. Following many decades of intensive theoretical and experimental study, it is now opportune to explore electron-transfer processes by way of modem computational chemistry. In essence, this requires the meaningful calculation of those thermodynamic parameters that combine to control the rate of electron-transfer between remote donor and acceptor species. The most important parameters are the nuclear and solvent re-organisation energies, the electronic coupling matrix element, the change in Gibbs free-energy and the activation energy change accompanying electron-transfer. Clearly, the surrounding environment has to be taken into account. Restricting attention to intramolecular electron-transfer in tripartite supermolecules of general type donor-bridge-acceptor (D-B-A), it is possible to compute each of the required thermodynamic properties from first principles. We examine here the most common quantum chemical approaches for estimation of each term and show that it is possible to arrive at a realistic estimate of the overall rate of electron-transfer. Attention is focused on readily accessible computational methodology. (C) 2003 Japanese Photochemistry Association. Published by Elsevier B.V. All rights reserved.