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

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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.