Current-Voltage Characteristics of a Molecule with Isolated Frontier Orbitals

Formation of the current through a molecule with two terminal groups is studied on the assumption that these groups exhibit themselves as donor and acceptor sites with respect to the electrodes. It is shown that the hopping and tunnel charge transfer mechanisms are generally responsible for the current formation, but the efficiency of a tunnel charge transmission is controlled by a hopping one via a molecular charging. An analytic expression for the current is derived, and the experimental data are explained. It is shown that, in the pre-resonant voltage region, even the simplest single-level version of the theory can describe the experiment with a rather good accuracy.