電子構造計算による各種フラーレンの物性理解と物質設計

本文研究了面心立方固态C_（60）经加压热处理后所形成的聚合C_（60）相的电子结构和能量。有趣的是，发现这些聚合的C60相与fcc固体C60一样稳定或甚至比fcc固体C60更稳定。在电子学上，发现它们具有半导体输运性质，基本禁带比fcc固体C60窄。除了这些已知的1-D和2-D聚合的C60相，我们研究了3-D聚合的C60相。由总能量计算，我们预测在单轴应力作用下，二维四面体聚合物相可以出现稳定的三维聚合的C_（60）。有趣的是，它可以是一种具有很大费米能级态密度的金属相。迄今为止，已经发现了几种具有体心晶格几何结构的Ba掺杂C60超导体，但与碱金属掺杂的fcc C60超导体不同，它们的电子结构还不清楚。本文在密度泛函理论的框架下研究了K_3Ba_3C_（60）和Rb_3Ba_3C_（60）bcc超导体的电子结构。发现C60态不仅与Ba杂化，而且与碱金属态杂化。这与fcc K3 C60和Rb 3C 60超导体形成鲜明对比，其中K或Rb状态不与C60状态杂化。我们还研究了Ba_4C_（60），这是迄今为止发现的第一个也是唯一一个非立方C_（60）超导体。我们还研究了碱金属掺杂碳纳米管和C_（60）掺杂碳纳米管的电子结构。在它们的费米能级电子结构中，近自由电子态有相当大的贡献。

We have studied the electronic structure and the enegetics of the polymerized C60 phases which can be produced by a heat treatment of fcc solid C60 under pressure. Interestingly, these polymerized C60 phases are found to be as stable as or even more stable than fcc solid C60. Electronically they are found to have semiconducting transport properties with narrower fundamental gap than fcc solid C60. In addition to these known 1-D and 2-D polymerized C60 phases, we investigated the 3-D polymerized C60 phase. From the total energy calculation, we predict that there can appear stable 3-D polymerized C60 if 2-D tetragonal polymer phase is treated under uniaxial stress. Interestingly, it can be a metallic phase with very large Fermi-level density of states.So far several Ba-doped C60 superconductors with body-centered lattice geometry have been found. However, their electronic structure is not yet known well unlike the alkali-doped fcc C60 superconductors. We have studied the electronic structure of K3Ba3C60 and Rb3Ba3C60 bcc superconductors in the framework of the density-functional theory. The C60 states are found to hybridize with not only Ba but also alkali states. This is in sharp contrast with the fcc K3C60 and Rb3C60 superconductors where K nor Rb states are not hybridized with C60 states. Also we studied the Ba4C60, the first and only non-cubic C60 superconductor found so far. The Fermi surface is found to be highly anisotropic.We also studied the electronic structure of alkali-doped carbon nanotube and C60 doped carbon nanotube. In their electronic structure at the Ferimi level the nearly-free electron states are found to give considerable contribution.