| Abstract
| - Ten different regioisomers of C60 trimers with intact cages were studied using the empirical tight-binding(TB) total energy calculation and the semiempirical PM3, AM1, and MNDO methods. We determined thestable atomic structure and energies of 10 (C60)3 regioisomers with ETBTEC, PM3, AM1, and MNDOcalculations. The dimerization of C60 is exothermic according to the density-functional-based nonorthogonaltight-binding (DF-TB) method; the semiempirical PM3, AM1, and MNDO; and the ab initio 3-21G LDA andHF calculations, but it is endothermic in both the TB and the ab initio B3LYP6-31G*//4-21G B3LYPcalculations. Therefore, according to the TB calculations, the most stable regioisomer of C60 trimers is equatorial.The energies of the trans-3(C2), trans-1(D2h), trans-2(C2), trans-4(Cs), cis-1 (C3ν), cis-2(Cs), cis-3(C2),cis-1(Cs), and cis-2(C3ν) regioisomers relative to the equatorial regioisomer are 13,19, 20, 30, 66, 99, 169,215, and 673 meV, respectively.
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