Theoretical Study of Quantum Conductance of Conjugated and Nonconjugated Molecular Wire Junctions

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• 作者：Run-Wen Yan ; Xi Jin ; Si-Yuan Guan ; Xia-Guang Zhang ; Ran Pang ; Zhong-Qun Tian ; De-Yin Wu ; Bing-Wei Mao
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：June 9, 2016
• 年：2016
• 卷：120
• 期：22
• 页码：11820-11830
• 全文大小：635K
• 年卷期：0
• ISSN：1932-7455

文摘

Electron transport through molecular junctions has been widely investigated experimentally and theoretically. Unfortunately, there exists discrepancy on the single molecular conductance between theoretical calculations and experimental measurements. In this paper, first-principle density functional theory combined with nonequilibrium Green’s function approach is employed; we studied electronic structures, molecular lengths, and interfacial interactions of three kinds of molecular junctions, alkanedithiols, oligo(1,4-phenylene-ethynylene)s, and 1,4-benzene-di(n-alkylthiol) (BDnT), embedding in nanogaps of gold electrodes. First, our approach can accurately describe the binding interaction between the thiol group and gold electrode so that the conductance of alkanedithiol in a gold junction can be well predicted. We found that a previous underestimation of HOMO–LUMO gaps in the junction system leads to the overestimated conductance for conjugate molecules with sulfur atoms binding to gold electrodes. In the study of BDnT molecular wires with a phenyl ring, our results show that the HOMO–LUMO gap reaches a constant with molecular length increasing. Moreover, a larger predicted conductance can be attributed to the overlapping between the nonbonding lone-paired orbital of sulfur atoms and the delocalized π electrons of the phenyl ring. Finally, we found that the conductance of molecules with short length or conjugated electronic structure greatly relies on the interfacial configuration. We proposed that these findings can give a clear understanding of electron transport in junction systems and open a promising theoretical study of molecular electronics.