Difficulty of the evaluation of the barrier height of an open-shell transition state between closed shell minima: The case of small C-4n rings - Université de Rennes Accéder directement au contenu
Article Dans Une Revue Journal of Chemical Physics Année : 2022

Difficulty of the evaluation of the barrier height of an open-shell transition state between closed shell minima: The case of small C-4n rings

Résumé

C-4n cyclacenes exhibit strong bond-alternation in their equilibrium geometry. In the two equivalent geometries, the system keeps an essentially closed-shell character. The two energy minima are separated by a transition state suppressing the bond-alternation, where the wave function is strongly diradical. This paper discusses the physical factors involved in this energy difference and possible evaluations of the barrier height. The barrier given as the energy difference between the restricted density functional theory (DFT)/B3LYP for the equilibrium and the broken symmetry DFT/B3LYP of the transition state is either negative or small, in contradiction with the most reliable Wave Function Theory calculations. The minimal (two electrons in two molecular orbitals) Complete Active Space self-consistent field (CASSCF) overestimates the barrier, and the subsequent second-order perturbation cancels it. Due to the collective character of the spin-polarization effect, it is necessary to perform a full pi CASSCF + second-order perturbation to reach a reasonable value of the barrier, but this type of treatment cannot be applied to large molecules. DFT procedures treating on an equal foot the closed-shell and open-shell geometries have been explored, such as Mixed-Reference Spin-Flip Time-dependent-DFT and a new spin-decontamination proposal, namely, DFT-dressed configuration interaction, but the results still depend on the density functional. M06-2X without or with spin-decontamination gives the best agreement with the accurate wave function results. Published under an exclusive license by AIP Publishing.

Domaines

Chimie
Fichier principal
Vignette du fichier
David et al - 2022 - Difficulty of the evaluation of the barrier height.pdf (1.2 Mo) Télécharger le fichier
Origine : Fichiers produits par l'(les) auteur(s)

Dates et versions

hal-03711124 , version 1 (20-07-2022)

Identifiants

Citer

Grégoire David, Gregoire David, Nadia Ben Amor, Tao Zeng, Nicolas Suaud, et al.. Difficulty of the evaluation of the barrier height of an open-shell transition state between closed shell minima: The case of small C-4n rings. Journal of Chemical Physics, 2022, 156 (22), pp.224104. ⟨10.1063/5.0090129⟩. ⟨hal-03711124⟩
47 Consultations
62 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More