Fading Memory in the Theory of Electronic Excitation Transfer

Within the framework of a model with the Hamiltonian of the electron–phonon interaction linear in the phonon operators, a memory function (MF) has been found which represents a kernel of the integral operator in a generalized master equation describing the migration of the electronic excitations in the crystal. At finite temperatures the microscopic elements of MF obtained fade in time. This is due to the presence of phonon‐assisted transitions which are competing with the zero‐phonon one. Therefore, the coarse‐grained MF has two characteristic fading times.