Thermopower of Amine - Gold-Linked, Aromatic Molecular Junctions from First Principles

Using a self energy corrected scattering state approach based on density functional theory (DFT), we explain recent measurements of the thermopower or the Seebeck coefficient S, for oligophenyldiamine-gold single molecule junctions and show that they are consistent with separate measurements of their electrical, conductance, G. Our calculations with self-energy corrections to the OFT electronic states in the junction predict low bias Sand 6 values in good quantitative agreement with experiments. We find S varies linearly with the number of Phenyls N, with a gradient beta(s) of 2.1 mu V/K, in excellent agreement with experiment In contrast OFT calculations without self energy corrections overestimate both S and beta(s) (with a DFT value for beta(s) three times too large). While beta(s) is found to be a robust quantity Independent of junction geometry, the computed values of S show significant sensitivity to the contact atomic structure-more so than the computed values of G. This observation is consistent with the experimentally measured spreads in S and G for amine-Au junctions: Taken together With previous computations of the electrical conductance (as reported in Quek, S.Y.; et al., Nano Lett. 2009, 9, 3949), our calculations of S conclusively demonstrate, for the first time, the consistency of two complementary yet distinct measurements of charge transport through single-molecule junctions and substantiate the hied for an accurate treatment of junction electronic level alignment to describe off-resonant tunneling in,these junctions.