Polarization of metallic carbon nanotubes from a model that includes both net charges and dipoles
Polarization of metallic carbon nanotubes from a model that includes both net charges and dipoles
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DOI：
10.1103/physrevb.71.235333
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发表时间：
2005-06-01
影响因子：
3.7
通讯作者：
Mayer, A
中科院分区：
文献类型：
--
作者：
Mayer, A
一种常用的测定碳纳米管极化的方法是给每个原子配一个偶极子，考虑到外场和与其他偶极子的相互作用，偶极子的值可以自洽地计算出来。我们在这里扩展这种半经验描述，把净电荷和偶极子与每个原子联系起来。考虑到除偶极子外的净电荷，使人们能够解决电子响应于外场从分子的一部分移动到另一部分的事实。它还使人们能够解释额外费用的积累。这些效应实际上发生在任何金属结构中，仅依靠偶极子的模型很难解释。在此，我们提出了一种计算方案来确定这些电荷和偶极子，这是基于该系统的总静电能量最小的要求。作为一个应用，我们研究了（5,5）纳米管的极化，该纳米管要么是孤立的，要么是靠近金属表面，要么是直接接触金属表面，这是场发射模拟所需要的。与只考虑偶极子的模型相比，这种技术能更好地描述这种纳米管的金属丰度。它也使人们能够解释化学势在与金属支撑物的背接触处的平衡。
A technique commonly used to determine the polarization of carbon nanotubes is to associate with each atom a dipole, whose value is computed self-consistently considering the external field and the interactions with the other dipoles. We extend here this semi-empiric description by associating with each atom both a net electric charge and a dipole. Considering net charges in addition to the dipoles enables one to address the fact that electrons move from one part of the molecule to the other in response to an external field. It also enables one to account for the accumulation of extra charges. Those effects, which actually occur in any metallic structure, are poorly accounted for by models that rely on dipoles only. We propose here a computational scheme to determine those charges and dipoles based on the requirement that the total electrostatic energy of this system is minimized. As an application, we study the polarization of a (5,5) nanotube, which is either isolated, close to a metallic surface, or in direct contact with it, as required for simulations of field emission. Compared to the model wherein only dipoles are considered, this technique gives a better account of the metallicity of this kind of nanotube. It also enables one to account for the equilibration of the chemical potentials at the back contact with the metallic support.