Many-body treatment of quantum transport through single molecules

We investigate multi-terminal quantum transport through single molecules including intramolecular correlations exactly by using the nonequilibrium Green function approach, but treating the lead-molecule coupling perturbatively via a Dyson expansion \footnote{Cardamone D. et al. Nano Lett. Vol 6 2422, 2006}, with an extended Pariser--Parr--Pople molecular model. As a validation of the theory we calculate the linear and non-linear transport properties of 1,4-Benzenedithiol(BDT) and compare these results to experiment\footnote{Xiao X. et al. Nano Lett. Vol 4 267, 2004}. We find many transport features which are not accessible via meanfield approaches such as Coulomb Blockade steps and an incipient Hubbard-Mott insulator gap. We also calculated the thermopower exactly and find, in accordance with recent experimental\footnote{Reddy P. et al. Science. Vol 315 1568, 2007} and theoretical reports, that the transport in this junction is dominated by holes (p-type). This result allowed us to then extract the remaining free parameter, the lead-molecule coupling $\Gamma$. The resulting nonlinear I-V curve was found to be in good quantitative agreement with experiment. Finally, we calculated the differential conductance as a function of gating and bias potential to construct a full molecular `Coulomb diamond'.