Extending Ovchinnikovs Rule to Search for Bistable Hydrocarbons

4 Extending Ovchinnikov s Rule to Search for Bistable Hydrocarbons 

The spin-Hamiltonian VB theory is a very simple and easy-to-use semiempi-rical tool that is based on the molecular graph. It is consistent with the VB theory described in Chapter 3, albeit with some simplifying assumptions and a more limited domain of application. Typically, this theory deals with the neutral ground or excited states of conjugated molecules or other homonuclear assemblies with one electron per site. For large systems, it reproduces the results of PPP full Cl, while dealing with a much smaller Hamiltonian matrix. 

This theory also possesses an ab initio based quantitative version (10,19), in which the parameters are geometry dependent and fitted on accurately calculated potential surfaces of ethylene. Despite its simplicity, the spin-Hamiltonian theory has proven itself to be accurate for predicting ground state, as well as excited state, properties and transition energies. 

Cooper, Ed., Valence Bond Theory, Chapters 15-23, Elsevier, New York, 2002. 

Hubbard, Proc. Roy. Soc. London, Ser. A 276, 238 (1963). Electron Correlations in Narrow Energy Bands. 

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