Jin, Chengjun1; Markussen, Troels2; Thygesen, Kristian Sommer3
1 Center for Atomic-scale Materials Design, Center, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 Center for Nanostructured Graphene, Center, Technical University of Denmark
We investigate the electronic conductance and thermopower of a single-molecule junction consisting of bis-(4-aminophenyl) acetylene (B4APA) connected to gold electrodes. We use nonequilibrium Green's function methods in combination with density-functional theory (DFT) and the many-body GW approximation. To simulate recent break junction experiments, we calculate the transport properties of the junction as it is pulled apart. For all junction configurations, DFT with a standard semilocal functional overestimates the conductance by almost an order of magnitude, while the thermopower is underestimated by up to a factor of 3, except for the most highly stretched junction configurations. In contrast, the GW results for both conductance and thermopower are in excellent agreement with experiments for a wide range of electrode separations. We show that the GW self-energy not only renormalizes the molecular energy levels but also the coupling strength. The latter is a consequence of the finite response time associated with the electronic screening in the metal electrodes.
Physical Review B (condensed Matter and Materials Physics), 2014, Vol 90, Issue 7