Department of Chemistry and the Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
J Chem Phys. 2013 Mar 21;138(11):114706. doi: 10.1063/1.4795496.
We report a theoretical study of the thermopower of single-molecule junctions with focus on phenyl-based molecular junctions. In contrast to prior studies, thermal fluctuations of the torsional angle between the phenyl rings and variations in the position of the molecular level alignment with respect to the electrode Fermi energy were taken into account. Full thermopower histograms were obtained, and their dependence on the magnitude of the fluctuations was studied. We found that at large molecular orbital variations, the thermopower becomes strongly dependent on the torsion angle and can even change sign. This results in a marked effect of fluctuations on the thermopower distribution, yielding an average thermopower at high temperatures that differs (smaller or larger) from the fluctuation-free value, depending on the strength of fluctuations. We therefore conclude that fluctuations should be taken into account both when extracting single-molecule parameters, such as the molecular level-Fermi level offset, and in predictions of the thermopower of molecular junctions.
我们报告了对具有苯基分子结的单分子结的热电势的理论研究。与先前的研究不同，我们考虑了苯环之间的扭转角的热波动以及分子能级相对于电极费米能的位置的变化。我们获得了完整的热电势直方图，并研究了它们对波动幅度的依赖性。我们发现，在分子轨道变化较大的情况下，热电势对扭转角变得非常依赖，甚至可以改变符号。这导致波动对热电势分布有显著影响，在高温下产生的平均热电势与无波动时的值不同（更小或更大），具体取决于波动的强度。因此，我们得出结论，在提取分子参数（例如分子能级-费米能级偏移）和预测分子结的热电势时，都应该考虑到波动。
