Barrier formation and charging energy for a variable nanogap organic molecular junction: a tip/C60/Au(111) configuration.

We analyze the nanogap organic molecular junction formed by a C(60) molecule in between an Au-tip and an Au(111)-surface. In our approach, we first calculate the atomic geometry of the tip/C(60)/Au(111) nanocontact as a function of the tip-surface distance and molecule adsorption site using a density functional theory-local density approximation (DFT-LDA) technique. The electronic structure and metal/organic barrier height formation (for a single molecule) are analyzed using the induced density of interface states model for metal/organic interfaces. From this analysis we calculate the charging energy U(eff) of the C(60) molecule at the nanocontact and determine self-consistently the transport energy gap and the organic molecule density of states. Our results are shown to be in good agreement with the experimental evidence.