Reference system master equation approaches to condensed phase charge transfer processes. I. General formulation

Two complimentary master equation approaches for the study of condensed phase charge transfer processes are developed. The first approach is appropriate when the (diabatic) activation energy is larger than the electronic coupling strength, and thus localized tight binding states form a zeroth-order set of electronic states. The second approach, the pure dephasing reference system (PDRS) master equation method, is designed to study the case where charge is delocalized over the donor and acceptor sites, and a zeroth-order set of quasiadiabatic states are used as a reference system. It is argued that a large majority of the electron transfer parameter space may be accurately covered with these two methods. Particular emphasis is placed on the treatment of nonequilibrium initial preparation, short-time nonexponential behavior, and backflow. The methods outlined in this work are general enough to treat anharmonic environments. A semiclassical implementation of the master equation approaches appropriate for anharmonic environments is outlined. The relationship between the methods developed herein and previous work, including the nonequilibrium golden rule-type methods of Coalson and co-workers [J. Chem. Phys. 101, 436 (1994); 102, 5658 (1995)] is analyzed. The limitations of the methods are discussed. (C) 2001 American Institute of Physics.