Electron transfer and tunneling from donor to acceptor in anharmonic crystal lattices

Abstract

We model electron transfer from donor to acceptor with a lattice with non-uniform electron on-site energies. The electron motion is described in a tight binding approximation and the lattice site dynamics follows the Morse potential. We focus on the transition time from donor to acceptor which is first determined analytically for a rigid lattice and then numerically from computer simulations of the full system at low temperature. For the parameter ranges explored here a very good agreement is found between the analytical and the numerical transition times. Furthermore, this nonlinear model can account both for the order of magnitude and for the variation with distance of the transition times from donor to acceptor that are measured experimentally, even in the case of long range transitions, i.e., when the distances arewell beyond 20 Å. While for short distances and weakly bound electrons the transfer is of the non-tunneling type, for larger distances and/or strongly bound electrons the transfer is tunneling-like, with the transition time varying exponentially.