An extended Heisenberg model for conjugated hydrocarbons. II. Kekulé basis

We investigate the solution of a recently proposed [J. Chem. Phys. 117, 9977 (2002)] improved valence bond model in a basis of Kekulé functions. The model, which has the form of an extended Heisenberg Hamiltonian with next-nearest-neighbor and ring permutation terms, operates in the space of all cov...

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Veröffentlicht in:The Journal of chemical physics 2003-12, Vol.119 (21), p.11011-11016
Hauptverfasser: Wu, Jian, Schmalz, T. G., Klein, D. J.
Format: Artikel
Sprache:eng
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Zusammenfassung:We investigate the solution of a recently proposed [J. Chem. Phys. 117, 9977 (2002)] improved valence bond model in a basis of Kekulé functions. The model, which has the form of an extended Heisenberg Hamiltonian with next-nearest-neighbor and ring permutation terms, operates in the space of all covalent valence bond structures which grows very rapidly with molecular size. It is found that truncation of the basis to include only the very much smaller number of nearest-neighbor spin pairings, the Kekulé functions, yields better than 98% of the exact energy in most cases. Extensions to excited states are discussed. As an illustration of the applicability of the model to large molecules, we solve it for the ground and first excited Hu singlet state of C60 buckminsterfullerene, and obtain results in good agreement with other theoretical treatments. The model shows promise of being an easily applied semiquantitative valence bond model for large molecules.
ISSN:0021-9606
1089-7690
DOI:10.1063/1.1622659