Influence of Low-Symmetry Distortions on Electron Transport through Metal Atom Chains: When Is a Molecular Wire Really "Broken"?
Influence of Low-Symmetry Distortions on Electron Transport through Metal Atom Chains: When Is a Molecular Wire Really "Broken"?
复制标题
DOI：
10.1021/ja2028475
复制
发表时间：
2011-08-17
影响因子：
15
通讯作者：
McGrady, John E.
中科院分区：
文献类型：
--
作者：
Georgiev, Vihar P.;McGrady, John E.
在分子电子学领域，人们常常认为分子轨道的离域性和它们支持电流流动的能力之间有着密切的联系。而离域通常被认为是结构对称的同义词，例如，在沿着分子线的键的长度中。在这项工作中，我们使用密度泛函理论结合非平衡绿色的功能，以显示恰恰相反的是在扩展的金属原子链Cr-3（dpa）（4）（NCS）（2），其中离域π框架先前已被提出是占主导地位的导电途径。Cr-3核心的低对称性畸变确实降低了这些π通道的有效性，但这在很大程度上与低偏压下的电子输运无关，因为它们远低于费米能级。相反，主要的途径是通过sigma对称性的高阶轨道，即使是相当大的扭曲也基本上保持不变。事实上，电导实际上略微增加，因为sigma（nb）沟道向上朝向费米能级移位。这些计算表明，在这些金属链的结构和功能之间的微妙和违反直觉的关系，具有重要的意义，从扫描隧道和原子力显微镜实验中出现的数据的解释。
In the field of molecular electronics, an intimate link between the delocalization of molecular orbitals and their ability to support current flow is often assumed. Delocalization, in turn, is generally regarded as being synonymous with structural symmetry, for example, in the lengths of the bonds along a molecular wire. In this work, we use density functional theory in combination with nonequilibrium Green's functions to show that precisely the opposite is true in the extended metal atom chain Cr-3(dpa)(4)(NCS)(2) where the delocalized pi framework has previously been proposed to be the dominant conduction pathway. Low-symmetry distortions of the Cr-3 core do indeed reduce the effectiveness of these pi channels, but this is largely irrelevant to electron transport at low bias simply because they lie far below the Fermi level. Instead, the dominant pathway is through higher-lying orbitals of sigma symmetry, which remain essentially unperturbed by even quite substantial distortions. In fact, the conductance is actually increased marginally because the sigma(nb) channel is displaced upward toward the Fermi level. These calculations indicate a subtle and counterintuitive relationship between structure and function in these metal chains that has important implications for the interpretation of data emerging from scanning tunnelling and atomic force microscopy experiments.