Theory of electrical conduction through a molecule

We present a theoretical study of electronic transport through a 1,4 benzene-dithiolate (BDT) ion chemically bonded to two gold leads. The model consists of a single BDT attached to two Au clusters, which are in turn attached to ideal one-dimensional leads. Extended Huckel theory is used to model the electronic structure and the Lippmann-Schwinger equation is solved for the lead-to-lead transmission. The current-voltage characteristics of the system are calculated using the finite temperature, finite voltage Landauer formula. Different atomic configurations of the Au clusters are examined including the effects of thermally induced positional disorder of the Au atoms. We find that while in some cases there is conduction via states derived from the BDT HOMO and LUMO levels, conduction due to levels derived from hybrid Au cluster-BDT states often predominate. The current-voltage characteristics are found to be sensitive to the specific configuration of the Au clusters, BDT and ideal leads.