Twenty-four distinct structures of C-28 are considered theoretically using
Hartree-Fock theory, hybrid Hartree-Fock/density functional theory (B3LYP),
and second-order perturbation theory. The tetrahedral (5)A(2) State is con
firmed as the electronic ground state isomer. However, a second fullerene s
tructure, a singlet state of D-2 symmetry, is predicted to lie less than 2
eV above the expected global minimum. The relative energies of the various
C-28 isomers can be rationalized in terms of their structural features. (C)
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