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We have modified the ASED-MO parameters for C atom so as to yield the energy level correlation, optical transition gap, and proper structure for the previous results of C 60 . In order to study eight regioisomeric bisadducts of C 60 [Pt(PH 3 ) 2 ] 2 , we calculate the structure and electronic properties for monoadduct and each regioisomer of bisadducts and compare the relative stability with the ASED-MO method. Here equatorial and trans-3 regioisomers are more stable than the others. Our calculated results and point group suggest that the observation of only three isomers of [(Et 3 P) 2 Pt] 2 C 60 by the 31 P NMR would be explained by the three kinds of group isomers ( e, trans-3; C s ), ( trans-4, D 2h ), and ( trans-2, trans-1; C 2 ).

The construction of nanoscale devices is a potentially important area of technology. Recently a fullerene isoxazoline was reported as an example for nanoscale connectors in molecular electronic devices. By using the semiempirical PM3 calculation, we optimize the structures for fullerene isoxazolines and discuss the regiochemistry of the second addition of a nitrile oxide to a fullerene isoxazoline.

In order to study the electron doping effect on the neutral C60 dimer with the linkage through a [2+2] cycloaddition, structures of the neutral dimer and its dianion have been energetically optimized by the semiempirical Hamiltonian PM-3, The (C60)22− has turned out to have a slightly squashed and equatorially swollen geometry in each C60 compared to the structure of the (C60)2. But both have the same symmetry of D2h. The doped electrons in the dianion will be largely on an equator zone of each C60 ball. The intermolecular center-to-center distance is longer by about 0.03 angstrom in the C60 dimer dianion than in its neutral case.

Using the extended Huckel molecular orbital (EHMO) and the EH band calculation in connection with the tight-binding model, we have studied electronic structure and related properties of the charged cluster models relating to superconducting YBa 2 Cu 3 O 7−x crystals in which O-atoms in regular sites were selectively replaced with Cl atoms. In analogy to the isomorphism problem with molecules, we discuss all possible combinations of Cl-substitutions in O-sites with one, two, and four Cl atoms in our cluster calculation. It shows that the electronic structure of the symmetrically Cl-substituted YBCO is closer to that of the superconducting YBCO than that obtained from the unsymmetrical substitution. This applies in particular if O is replaced with Cl around the Cu(1) site. In both EHMO and EH band calculations for Cl-substitution around Cu(1) site, the decreasing order of charge density for each Cl site is Cl(4) > Cl(5) > Cl(1) which agrees with the result of NMR study.

The electronic structures of the C 60 , (H 3 P) 2 Pt(η 2 -C 2 H 4 ), and (H 3 P) 2 Pt(η 2 -C 60 ) are calculated by using the EHT-MO method with the fragment analysis. We have modified the EHT parameters so as to yield the energy level correlation and optical transition gap for the previous theoretical result of C 60 . In Pt-derivatives, our FMO results with the modified parameters show that the carbon-carbon double bonds of C 60 and ethene react like those of electron-poor arenes and alkenes. Back donation is much stronger in the C 60 complex than in the ethylene complex : the amount of charge transfer is about two times larger and the stabilization energy is about 0.24eV larger.

Using a tight-binding model with electron-phonon coupling based on the modified Su-Schriffer-Heeger model Hamiltonian, we obtained the deformed lattice structures for C603− which is charge-transfer state for superconducting M3C60 compounds. The deformed structures are Ci (λ=0.1, 0.3) and C2v (λ=0.5), which are different to D5d of C601− in the same values of λ. Here λ means the dimensionless coupling constant (S2/KT). We also have shown the bond length difference between C603− and C60.