Resolving a puzzling anomaly in the spin-coupled generalized valence bond description of benzene

Xu, Lu T, Cooper, David L ORCID: 0000-0003-0639-0794 and Dunning, Jr, Thom H (2020) Resolving a puzzling anomaly in the spin-coupled generalized valence bond description of benzene. Journal of Computational Chemistry, 41 (15). pp. 1421-1426.

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Abstract

In an earlier study of benzene, Small and Head-Gordon found that the spin-coupled generalized valence bond (SCGVB) wave function for the π system predicted a distorted (non-D6h) geometry, one with alternating CC bond lengths. However, the variations in the energy were very small and the predictions were made using a very small basis set (STO-3G). We re-examined this prediction using a much larger basis set (aug-cc-pVTZ) to determine the dependence of the energy of benzene on the distortion angle, ΔθCXC (ΔθCXC = 0° corresponds to the D6h structure). We also found a distorted geometry with the optimum ΔθCXC being 0.31° with an energy 0.040 kcal mol⁻¹ lower than that for the D6h structure. In the optimum geometry, adjacent CC bond lengths are 1.3861 Å and 1.4004 Å. Analysis of the SCGVB wave function led us to conclude that the cause of the unusual non-D6h geometry predicted by the SCGVB calculations seems to be a result of the interaction between the Kekulé and Dewar components of the full SCGVB wave function. The addition of doubly ionic configurations to the SCGVB wave function leads to the prediction of a D6h geometry for benzene and a dependence on ΔθCXC essentially the same as that predicted by the complete active space self-consistent field wave function.

Item Type:	Article
Uncontrolled Keywords:	benzene, Dewar structures, Kekulé structures, non-D6h structure, SCGVB
Depositing User:	Symplectic Admin
Date Deposited:	19 Oct 2020 10:39
Last Modified:	18 Jan 2023 23:27
DOI:	10.1002/jcc.26185
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3104593

Available Versions of this Item

• Resolving a puzzling anomaly in the spin‐coupled generalized valence bond description of benzene. (deposited 03 Mar 2020 15:46)
  • Resolving a puzzling anomaly in the spin-coupled generalized valence bond description of benzene. (deposited 19 Oct 2020 09:15)
    • Resolving a puzzling anomaly in the spin-coupled generalized valence bond description of benzene. (deposited 19 Oct 2020 10:39) [Currently Displayed]