In a recent paper Liang {\it et al.} [Nature {\bf 411}, 665 (2001)] showedexperimentally, that metallic nanotubes, strongly coupled to externalelectrodes, may act as coherent molecular waveguides for electronic transport.The experimental results were supported by theoretical analysis based on thescattering matrix approach. In this paper we analyze theoretically this problemusing a real-space approach, which makes it possible to control quality ofinterface contacts. Electronic structure of the nanotube is taken into accountwithin the tight-binding model. External electrodes and the central part(sample) are assumed to be made of carbon nanotubes, while the contacts betweenelectrodes and the sample are modeled by appropriate on-site (diagonal) andhopping (off-diagonal) parameters. Conductance is calculated by the Greenfunction technique combined with the Landauer formalism. In the plotsdisplaying conductance {\it vs.} bias and gate voltages, we have found typicaldiamond structure patterns, similar to those observed experimentally. Incertain cases, however, we have found new features in the patterns, like adouble-diamond sub-structure.
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机译：Liang {\ it et al。} [Nature {\ bf 411}，665（2001）]在最近的一篇论文中实验表明，与外电极紧密耦合的金属纳米管可以充当电子传输的相干分子波导。实验结果是基于散射矩阵方法的理论分析得到了支持。在本文中，我们使用实空间方法从理论上分析了此问题，这使得控制接口触点的质量成为可能。在紧密结合模型中考虑了纳米管的电子结构。假定外部电极和中心部分（样品）由碳纳米管制成，而电极和样品之间的接触则通过适当的现场（对角线）和跳跃（非对角线）参数建模。电导率是通过Greenfunction技术结合Landauer形式主义来计算的。在显示电导{\ it vs.}偏置和栅极电压的图中，我们发现了典型的菱形结构图案，与实验观察到的相似。但是，在某些情况下，我们在模式中发现了新功能，例如双钻石子结构。
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