ELECTRON-VIBRATIONAL EFFECTS IN THE TUNNEL CURRENT THROUGH POLYCENTRIC SYSTEMS

The conductivity of polynuclear cluster situated between two metallic electrodes is studied within the semiclassical approximation. The cond uctivity depends on the shape of adiabatic potential surface of 'clust er + excess electron' mixed-valence system which is entirely governed by the relationship between the intramolecular electron transfer and t he vibronic coupling. The specific cases of dimer and trimer molecules are illustrated through conductivity and current calculations. It is shown that localization --> delocalization transitions in mixed valenc e clusters are accompanied by more or less abrupt changes in the molec ular conductivity. However, the behavior of molecular conductivity and tunnel current is determined not only by the type of electronic distr ibution but also by the density of accessible electron-vibrational sta tes. (C) 1998 Elsevier Science B.V.