NEW EXPRESSION FOR THE EFFECTIVE TRANSFER-MATRIX ELEMENT IN LONG-RANGE ELECTRON-TRANSFER REACTIONS

A new expression for the effective transfer matrix element, T-DA, in l ong-range electron transfer is derived. This expression corrects the s econd-order perturbation theory estimate by accounting for an infinite number of terms in the perturbation expansion. The correction factors measure the extent of delocalization of the diabatic donor and accept or states. A simple procedure is devised to adjust the molecule to its transition state, which is the point of avoided crossing of the energ ies of the adiabatic states. The new expression is used to compute the half-splitting in these eigenenergies, which equals T-DA, without rec ourse to diagonalization. When checked against direct diagonalization for a truncated model of a ruthenium-modified azurin protein, this met hod located the point of avoided crossing and produced an estimate of the energy half-splitting which agreed with the result of diagonalizat ion with exceptional accuracy. (C) 1998 American Institute of Physics.