A complete active space valence bond (CASVB) method

Kimihiko Hirao, Haruyuki Nakano, Kenichi Nakayama, Michel Dupuis

Research output: Contribution to journalArticle

80 Citations (Scopus)

Abstract

A complete active space valence bond (CASVB) method is proposed which is particularly adapted to chemical interpretation. A CASVB wave function can be obtained simply by transforming a canonical CASSCF function and readily interpreted in terms of the well known classical VB resonance structures. The method is applied to the ground and excited states of benzene, butadiene, and the ground state of methane. The CASVB affords a clear view of the wave functions for the various states. The electronic excitation is represented in a VB picture as rearrangements of the spin couplings or as charge transfers which involve breaking covalent bonds and forming new ionic bonds. The former gives rise to covalent excited states and the latter to ionic excited states. The physical reasons why it is so difficult to describe the ionic excited states at the CASSCF level with a single active space and why the lowest 1 1B2 + state in cis-butadiene is so stabilized compared to the corresponding 1 1Bu + state in the trans isomer are easily identified in view of a VB picture. The CASVB forms a useful bridge from molecular orbital theory to the familiar concepts of chemists.

Original languageEnglish
Pages (from-to)9227-9239
Number of pages13
JournalJournal of Chemical Physics
Volume105
Issue number20
Publication statusPublished - 1996

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Excited states
valence
Wave functions
Ground state
excitation
butadiene
Covalent bonds
wave functions
Methane
Molecular orbitals
Benzene
Isomers
ground state
covalent bonds
Charge transfer
molecular orbitals
methane
isomers
benzene
charge transfer

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Hirao, K., Nakano, H., Nakayama, K., & Dupuis, M. (1996). A complete active space valence bond (CASVB) method. Journal of Chemical Physics, 105(20), 9227-9239.

A complete active space valence bond (CASVB) method. / Hirao, Kimihiko; Nakano, Haruyuki; Nakayama, Kenichi; Dupuis, Michel.

In: Journal of Chemical Physics, Vol. 105, No. 20, 1996, p. 9227-9239.

Research output: Contribution to journalArticle

Hirao, K, Nakano, H, Nakayama, K & Dupuis, M 1996, 'A complete active space valence bond (CASVB) method', Journal of Chemical Physics, vol. 105, no. 20, pp. 9227-9239.
Hirao, Kimihiko ; Nakano, Haruyuki ; Nakayama, Kenichi ; Dupuis, Michel. / A complete active space valence bond (CASVB) method. In: Journal of Chemical Physics. 1996 ; Vol. 105, No. 20. pp. 9227-9239.
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