Length dependence of conductance in aromatic single-molecule junctions

Using a scattering-state approach Incorporating self-energy corrections to the junction level alignment, the conductance G of oligophenyldiamine-Au junctions Is calculated and elucidated. In agreement with experiment, we find G decays exponentially with the number of phenyls with decay constant β = 1.7. A straightforward, parameter-free self-energy correction, including electronic exchange and correlations beyond density functional theory (DFT), is found to be essential for understanding the measured values of both G and β. Importantly, our results confirm quantitatively the picture of off-resonant tunneling In these systems and show that exchange and correlation effects absent from standard DFT calculations contribute significantly to β.