Magnetic Properties of Conjugated Hydrocarbons from Topological Hamiltonians

Malrieu, Jean‐Paul; Ferré, Nicolas; Guihéry, Nathalie

doi:10.1007/978-3-319-29022-5_14

Cited by 7 publications

(7 citation statements)

References 59 publications

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“…Alternatively, one may take a more deductive approach and rationalize the reactivity trends observed through comparison of the transformed orbitals of PQDM and MQDM to the SOMO of benzyl at Hückel level of theory. Such an analysis, which can be done analytically, has been performed in great detail by Malrieu and co-workers. − The results obtained this way are in line with the spin-density results discussed above, i.e., one retrieves significantly enhanced orbital amplitudes on the exocyclic methylene groups of PQDM etc.…”

Section: Diradical and Diradicaloid Reactivitysupporting

confidence: 73%

Do Diradicals Behave Like Radicals?

et al. 2019

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This review sets out to understand the reactivity of diradicals and how that may differ from monoradicals. In the first part of the review, we delineate the electronic structure of a diradical with its two degenerate or nearly degenerate molecular orbitals, occupied by two electrons. A classification of diradicals based on whether or not the two SOMOs can be located on different sites of the molecule is useful in determining the ground state spin. Important is a delocalized to localized orbital transformation that interchanges “closed-shell” to “open-shell” descriptions. The resulting duality is useful in understanding the dual reactivity of singlet diradicals. In the second part of the review, we examine, with a consistent level of theory, activation energies of prototypical radical reactions (dimerization, hydrogen abstraction, and addition to ethylene) for representative organic diradicals and diradicaloids in their two lowest spin states. Differences and similarities in reactivity of diradicals vs monoradicals, based on either a localized or delocalized view, whichever is suitable, are then discussed. The last part of this review begins with an extensive, comparative, and critical survey of available measures of diradical character and ends with an analysis of the consequences of diradical character for selected diradicaloids.

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Section: Diradical and Diradicaloid Reactivitysupporting

confidence: 73%

Do Diradicals Behave Like Radicals?

et al. 2019

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“…Approximate projection (AP), a PAV method proposed by Yamaguchi and co-workers, and other related spin-decontamination models by Malrieu and co-workers − have been successfully used in energy calculations of transition metal complexes and organic diradicals. ,, In a particularly intriguing report, Malrieu and Trinquier studied the effect of spin contamination on broken-symmetry singlet states of organic diradicals using a method they developed that estimates the optimized geometry of a spin-projected singlet using AP-like models . However, to the best of our knowledge, there has not yet been a systematic investigation of the impact of AP or related projection models on the geometries and subsequent property calculations of transition metal systems.…”

Section: Introductionmentioning

confidence: 99%

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model To Improve Density Functional Calculations

Sheng

Thompson

Hratchian

2019

J. Chem. Theory Comput.

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This work evaluates the quality of exchange coupling constant and spin crossover gap calculations using density functional theory corrected by the approximate projection model. Results show that improvements using the approximate projection model range from modest to significant. This study demonstrates that, at least for the class of systems examined here, spin projection generally improves the quality of density functional theory calculations of J-coupling constants and spin crossover gaps. Furthermore, it is shown that spin projection can be important for both geometry optimization and energy evaluations. The approximate projection model provides an affordable and practical approach for effectively correcting spin-contamination errors in such calculations.

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“…Ovchinnikov's statement was established from a magnetic (Heisenberg) picture of the π electron population, that is, from the strong correlation limit, but it may be reached whatever the electronic correlation versus delocalization ratio. 26,27 The magnetic properties of conjugated hydrocarbons attract an intense interest, 28 especially in view of spintronics applications. The ferromagnetic architectures receive a special interest, 28,29 but singlet diradicals also deserve attention from theoreticians 30−36 and experimentalists.…”

Section: Introductionmentioning

confidence: 99%

“…If the two numbers are equal, the ground state is therefore expected to be a singlet state, and the present study will be restricted to this case actually. Ovchinnikov’s statement was established from a magnetic (Heisenberg) picture of the π electron population, that is, from the strong correlation limit, but it may be reached whatever the electronic correlation versus delocalization ratio. , …”

Section: Introductionmentioning

confidence: 99%

Can a Topological Approach Predict Spin-Symmetry Breaking in Conjugated Hydrocarbons?

Malrieu

Trinquier

2016

J. Phys. Chem. A

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The closed-shell mean-field single determinants of large alternant hydrocarbons are frequently unstable with respect to a possible spin-symmetry breaking which produces different orbitals for the α and β electrons, either in Hartree-Fock or in Kohn-Sham DFT calculations. The present work shows that one may easily predict whether such a symmetry breaking will take place from the elementary topological Hückel Hamiltonian which introduces a simple hopping integral t. The demonstration makes use of the simplest representation of the bielectronic repulsion, namely, the Hubbard bielectronic operator, reduced to an on-site repulsion U, and takes benefit of the mirror theorem. A recipe is proposed to determine the relevant t/U ratio for a given exchange-correlation potential. The symmetry-breaking phenomenon first concerns the mixing between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), but it may eventually run on other pairs of mirror orbitals. These symmetry breakings may take place while the other molecular orbitals keep a closed-shell character. The spin polarization of these MOs, appearing in typical unrestricted mean-field calculations, is an induced and amplifying effect, which has to be distinguished from the symmetry breaking itself. Special attention is paid to the possible appearance of multiple symmetry breakings, leading to a polyradical character. The model is tested on six series of polycyclic hydrocarbons. This elementary approach sheds new arguments on the debate concerning the di- or polyradical character of polyacenes.

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Magnetic Properties of Conjugated Hydrocarbons from Topological Hamiltonians

Abstract: International audienc

Cited by 7 publications

References 59 publications

Do Diradicals Behave Like Radicals?

Do Diradicals Behave Like Radicals?

Assessing the Calculation of Exchange Coupling Constants and Spin Crossover Gaps Using the Approximate Projection Model To Improve Density Functional Calculations

Can a Topological Approach Predict Spin-Symmetry Breaking in Conjugated Hydrocarbons?

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