Multireference Configuration Interaction Methods – An Application to the Valence Isomerism in Cyclobutadieno-p-benzoquinone and its Diprotonated Form

Multireference averaged quadratic coupled cluster (MR-AQCC) calculations for cyclobutadieno-p-benzoquinone indicate that valence bond isomers 1a and 1b can exist as distinct species. The energy barrier height for their interconversion are 4.6 and 4.5 kcal [mol.sup.-1], respectively, what is by ca. 2...

Ausführliche Beschreibung

Gespeichert in:
Bibliographische Detailangaben
Veröffentlicht in:Croatica Chemica Acta 2015-12, Vol.88 (4), p.495-503
Hauptverfasser: Vazdar, Mario, Eckert-Maksić, Mirjana
Format: Artikel
Sprache:eng
Schlagworte:
Online-Zugang:Volltext
Tags: Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
Beschreibung
Zusammenfassung:Multireference averaged quadratic coupled cluster (MR-AQCC) calculations for cyclobutadieno-p-benzoquinone indicate that valence bond isomers 1a and 1b can exist as distinct species. The energy barrier height for their interconversion are 4.6 and 4.5 kcal [mol.sup.-1], respectively, what is by ca. 2 kcal [mol.sup.-1] lower than in the parent cyclobutadiene, implying that they could perhaps exist only under extreme conditions, namely at very low temperatures. For double protonated cyclobutadieno-p-benzoquinone, the CASSCF calculations erroneously predict existence of two valence isomers, 2a and 2b, whereas the MR-AQCC calculations reveal that geometry of the double protonated species could be best described by structure 2b. This nicely illustrates the crucial role of dynamic correlation and the need for using a highly-correlated theoretical method including geometry optimization in studied molecules. Keywords: cyclobutadieno-p-benzoquinone, multrireference calculations, valence isomerism, energy barriers.
ISSN:0011-1643
1334-417X
DOI:10.5562/cca2770