Molecular junctions hold great potential for future microelectronics, while the practical utilization has long been limited by the problem of conformational deformation during charge transport. Here we present a first-principles theoretical study on the surface-enhanced Raman spectroscopy (SERS) characterization of the p-terphenyl-4,4″-dithiol molecule and its 2,2′,5′,2″-tetramethylated analogue in gold junctions to investigate the molecular deformation mechanism. The effects of charge injection and external electric field were examined, both of which could change π-conjugation by varying the dihedral angle between the central and ending rings (D_IPT). The induced significant structural deformations then change SERS responses. Only the SERS responses under an external electric field can account for the experimentally observed Raman spectra, and those of charge injections cannot. Moreover, applying a strong electric field could enlarge the conductivities of the two molecular junctions, agreeing well with experiments. This information not only elaborates that the electric field effect constitutes one important mechanism for molecular deformation but also provides useful insights for the control of charge transport in molecular junctions.

中文翻译：

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金接界中2,2'，5'，2''-四甲基化的对-Terphenyl-4,4''-二硫醇分子变形的机理研究。

分子结在未来的微电子学中具有巨大的潜力，而长期以来的实际应用受到电荷传输过程中构象变形问题的限制。在这里，我们对金中的对-叔苯基-4,4″-二硫醇分子及其2,2'，5'，2''-四甲基化类似物的表面增强拉曼光谱（SERS）表征进行了第一性原理研究。研究分子连接的变形机理。研究了电荷注入和外部电场的影响，它们都可以通过改变中心环和末端环之间的二面角来改变π共轭（D _IPT）。然后，引起的明显结构变形会改变SERS响应。只有在外部电场下的SERS响应才能解释实验观察到的拉曼光谱，而电荷注入的则不能。此外，施加强电场可以扩大两个分子结的电导率，与实验吻合得很好。该信息不仅说明了电场效应构成了分子变形的一种重要机理，而且还为控制分子结中的电荷传输提供了有用的见识。