Relations Among the Models

An instructive view of the relation between the spectra of the Htickel model (U=0), the Heisenberg model (U large) and the Hubbard model is provided in Fig. 1. Those states described by the Heisenberg model are all of covalent 

In the following sections results will be reported of conjugated circuit calculations on a variety of fullerenes, of Heisenberg calculations on buckminsterfullerene, some of its isomers and derivatives, and a few smaller fullerenes, and of Hubbard/PPP calculations primarily on buckminsterfullerene, while attempting to emphasize both the strengths and the limitations of the VB picture of these molecules. 

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