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

Bibliographische Detailangaben
Veröffentlicht in:	Journal of computational chemistry. - 1984. - 41(2020), 15 vom: 05. Juni, Seite 1421-1426
1. Verfasser:	Xu, Lu T (VerfasserIn)
Weitere Verfasser:	Cooper, David L, Dunning, Thom H Jr
Format:	Online-Aufsatz
Sprache:	English
Veröffentlicht:	2020
Zugriff auf das übergeordnete Werk:	Journal of computational chemistry
Schlagworte:	Journal Article Dewar structures Kekulé structures SCGVB benzene non-D6h structure

Beschreibung
Zusammenfassung:	© 2020 Wiley Periodicals, Inc. 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
Beschreibung:	Date Revised 28.04.2020 published: Print-Electronic Citation Status PubMed-not-MEDLINE
ISSN:	1096-987X
DOI:	10.1002/jcc.26185