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Ionization energy and reduction potential in ferrocene derivatives. The effect of the exact exchange fraction in hybrid-DFT methods.
  • Mateja Toma,
  • Tea Kuvek,
  • Valerije Vrček
Mateja Toma
University of Zagreb Faculty of Pharmacy and Biochemistry
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Tea Kuvek
University of Zagreb Faculty of Pharmacy and Biochemistry
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Valerije Vrček
University of Zagreb Faculty of Pharmacy and Biochemistry
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Peer review status:UNDER REVIEW

18 Jun 2020Submitted to International Journal of Quantum Chemistry
19 Jun 2020Assigned to Editor
19 Jun 2020Submission Checks Completed
10 Jul 2020Reviewer(s) Assigned

Abstract

Hybrid density functionals have been regularly applied in state-of-the-art computational models for predicting reduction potentials. Benchmark calculations of the absolute reduction potential of ferricenium/ferrocene couple, the IUPAC-proposed reference in nonaqueous solution, include the B3LYP/6-31G(d)/LanL2TZf protocol. We used this procedure to calculate ionization energies and reduction potentials for a comprehensive set of ferrocene derivatives. The protocol works very well for a number of derivatives. However, a significant discrepancy (> 1 V) between experimental and calculated data was detected for selected cases. Three variables were assessed to detect an origin of the observed failure: density functional, basis set, and solvation model. It comes out that the Hartree-Fock exchange fraction in hybrid-DFT methods is the main source of the error. The accidental errors were observed for other hybrid models like PBE0, BHandHLYP, and M06-2X. Therefore, hybrid DFT methods should be used with caution, or pure functionals (BLYP or M06L) may be used instead.