title: Thermopower of amine-gold-linked aromatic molecular junctions from first principles.
abstract: 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 DFT electronic states in the junction predict low-bias S and G values in good quantitative agreement with experiments. We find S varies linearly with the number of phenyls N, with a gradient β(S) of 2.1 μV/K, in excellent agreement with experiment. In contrast, DFT calculations without self-energy corrections overestimate both S and β(S) (with a DFT value for β(S) three times too large). While β(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 need for an accurate treatment of junction electronic level alignment to describe off-resonant tunneling in these junctions.
authors.affiliation: Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, California 94720, United States.
authors.forename: Su Ying
authors.initials: SY
authors.lastname: Quek
authors.forename: Hyoung Joon
authors.initials: HJ
authors.lastname: Choi
authors.forename: Steven G
authors.initials: SG
authors.lastname: Louie
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Neaton