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Structure of [18]Annulene Revisited: Challenges for Computing Benzenoid Systems.
King, Rollin A; Schreiner, Peter R; Crawford, T Daniel.
Afiliación
  • King RA; Department of Chemistry, Bethel University, St. Paul, Minnesota 55112, United States.
  • Schreiner PR; Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, Giessen 35392, Germany.
  • Crawford TD; Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States.
J Phys Chem A ; 128(6): 1098-1108, 2024 Feb 15.
Article en En | MEDLINE | ID: mdl-38306465
ABSTRACT
For cyclic conjugated structures, erratic computational results have been obtained with Hartree-Fock (HF) molecular orbital (MO) methods as well as density functional theory (DFT) with large HF-exchange contributions. In this work, the reasons for this unreliability are explored. Extensive computations on [18]annulene and related compounds highlight the pitfalls to be avoided and the due diligence required for such computational investigations. In particular, a careful examination of the MO singlet-stability eigenvalues is recommended. The appearance of negative eigenvalues is not (necessarily) problematic, but near-zero (positive or negative) eigenvalues can lead to dramatic errors in vibrational frequencies and related properties. DFT approaches with a lower HF admixture generally appear more robust in this regard for the description of benzenoid structures, although they may exaggerate the tendency toward planarity and C-C bond-equalization. For the iconic [18]annulene, the results support a nonplanar equilibrium structure. The density-fitted frozen natural orbital coupled-cluster singles and doubles with perturbative triples [DF-FNO CCSD(T)] method of electron correlation with an aug-pVQZ/aug-pVTZ basis set places the C2 global minimum 1.1 kcal mol-1 below the D6h stationary point.

Texto completo: 1 Base de datos: MEDLINE Idioma: En Revista: J Phys Chem A Asunto de la revista: QUIMICA Año: 2024 Tipo del documento: Article

Texto completo: 1 Base de datos: MEDLINE Idioma: En Revista: J Phys Chem A Asunto de la revista: QUIMICA Año: 2024 Tipo del documento: Article