Consistent spin decontamination of broken-symmetry calculations of diradicals

The Journal of Chemical Physics
Grégoire DavidJean-Paul Malrieu

Abstract

Broken-symmetry calculations of diradicals exploit the mean-field energies of determinants that are not eigenfunctions of the Ŝ2 operator, the mean value of which is close to 1 for the ms = 0 solution. This spin contamination must be corrected. Two different contributions affect ⟨Ŝ2⟩, namely, the mixing between neutral and ionic valence bond components, the so-called kinetic exchange, which decreases ⟨Ŝ2⟩, and the spin polarization of the supposedly closed shell orbitals, which increases ⟨Ŝ2⟩. The popular Yamaguchi formula is valid for the first effect but irrelevant for the second one. From a few constrained broken-symmetry calculations, one may treat separately the two contributions and apply their specific spin decontamination correction. This work proposes a consistent spin-decontaminated procedure for the evaluation of singlet-triplet gaps in diradicals.

References

Feb 17, 2011·The Journal of Chemical Physics·Takashi Tsuchimochi, Gustavo E Scuseria
Jul 31, 2012·The Journal of Physical Chemistry. a·Jean-Paul Malrieu, Georges Trinquier
Feb 19, 2015·Physical Chemistry Chemical Physics : PCCP·Nicolas FerréJean-Paul Malrieu
Dec 23, 2017·The Journal of Physical Chemistry. a·Georges Trinquier, Jean-Paul Malrieu
Oct 9, 2019·Chemical Reviews·Thijs StuyverRoald Hoffmann
Aug 11, 2020·The Journal of Chemical Physics·Grégoire DavidJean-Paul Malrieu

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Citations

May 6, 2021·The Journal of Physical Chemistry. a·Ashima BajajMd Ehesan Ali

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