All matrix elements are expressed in the basis of energy eigenstates of the uncoupled donor or acceptor, in which the matrix representations of Ĥ0,A and Ĥ0,D are diagonal. Implicit in Eqs. (3) and ( ) is the assumption that the donor and acceptor interact only through their transition dipole moments. The associated dipole potential operators are twobody operators, in which case correct equations of motion for the one-body density matrices, ρ D and ρ A , should depend on a two-body donoracceptor density matrix. We eliminate the dependence of the equations of motion on the twobody density matrix by further assuming that the transition dipoles of the acceptor interacts only with the instantaneous expectation value of the dipole moment of the donor and vice versa. The interaction potential operator for the donor, in atomic units, is then given by