Extended Hartree-Fock (EHF) theory in chemical reactions

Yamaguchi, Kizashi; Yoshioka, Yasunori; Takatsuka, Tsutomu; Fueno, Takayuki

doi:10.1007/bf00549018

Cited by 75 publications

(62 citation statements)

References 28 publications

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“…where θ is the orbital mixing parameter [16]. The BS orbitals ψ ± are reduced to SOMOs of the left and right allyl radicals, while ψ 0 becomes equivalent to SOMO of the central allyl radical at the dissociation limit (θ = 45…”

Section: Allyl Radical Trimermentioning

confidence: 99%

“…The total energy of the singlet state after our approximate spin projection (AP) [2,16,32,33,37] is given by…”

Section: Analytic Expressions Broken Symmetry and Spin Projectionmentioning

confidence: 99%

“…), which are usually eliminated by spin projection techniques by Löwdin [1,2]. In another series of articles, we have investigated both spin unprojected and projected BS approaches at UHF and post-UHF levels such as UCCSD(T) [2,16,17]. The computational results of potential curves for several TS models by those BS methods are compared with those of SA methods such as CASSCF and CASPT2 [18].…”

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confidence: 99%

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Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Yamaguchi

Kawakami

Takano

et al. 2002

Int J of Quantum Chemistry

123

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Analytical expressions of total energies, effective exchange integrals, polyradical character, spin density, unpaired electron density, and information entropy are derived for allyl radical dimers and trimers on the basis of the Hubbard model in order to elucidate interrelationships among several broken-symmetry and symmetry-adapted approaches to molecular magnetism. Ab initio unrestricted Hartree-Fock and hybrid density functional theory (DFT) calculations of allyl radical dimers to decamers are also carried out for confirmation of characteristics revealed by the analytical investigations. A mesoscopic hydrogen radical cluster with 50 radical sites is studied by the ab initio hybrid DFT methods to elucidate functional behaviors of the above quantities with change of interatomic distance. The potential curves for the lowest and highest spin states of the cluster by these methods are depicted for the purpose. Implications of the present computational results are discussed in relation to size-consistent spin projection and size effects on effective exchange interactions in mesoscopic radical clusters.

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Section: Allyl Radical Trimermentioning

confidence: 99%

“…The total energy of the singlet state after our approximate spin projection (AP) [2,16,32,33,37] is given by…”

Section: Analytic Expressions Broken Symmetry and Spin Projectionmentioning

confidence: 99%

mentioning

confidence: 99%

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Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Yamaguchi

Kawakami

Takano

et al. 2002

Int J of Quantum Chemistry

123

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“…A way to estimate the coupling constant J by using Landé's rule in conjunction with E HS and E BS was put forward a long time ago (11,12,25), which is concisely reformulated and extended here. The HS and BS states are single-determinant states characterized by parallel and antiparallel alignment of spins on the two coupled paramagnetic sites, respectively.…”

Section: Binuclear Clustersmentioning

confidence: 99%

Dynamical magnetostructural properties of Anabaena ferredoxin

Schreiner

Nair

Pollet

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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A mixed quantum/classical investigation of the dynamical magnetostructural properties, that is, ''magnetodynamics,'' of oxidized Anabaena PCC7119 ferredoxin is carried out at room temperature in two distinct conformational states. This protein hosts a [2Fe-2S] cluster in which two iron centers are antiferromagnetically coupled to an overall low-spin electronic ground state that has a genuine multireference character. To study the magnetodynamics of this prosthetic group, an approximate spin projection method is formulated in the framework of density functional theory that allows for multideterminant ab initio molecular dynamics simulations to be carried out efficiently. By using this scheme, the influence of both thermal fluctuations and conformational motion on the structure of the [2Fe-2S] cluster and on the dynamics of the antiferromagnetic coupling constant, J(t), has been investigated. In addition to demonstrating how sensitively the shape of the [2Fe-2S] core itself is affected by hydrogen bonding, the analyses reveal a complex dynamical coupling of J to both local vibrations and large-amplitude motion. It is shown that this interplay can be understood in terms of specific vibrational modes and distinct hydrogen-bonding patterns between the iron-sulfur cluster and the protein backbone, respectively. This implies going beyond the Goodenough-Kanamori rules for angular magnetostructural correlations of oxidized iron-sulfur prosthetic groups.exchange coupling ͉ extended broken-symmetry ͉ hydrogen bonding ͉ iron-sulfur protein ͉ multideterminant hybrid molecular dynamics I ron-sulfur clusters are among the most ubiquitous, functionally versatile, and ancient prosthetic groups in proteins (1-4). One of the major classes of mobile electron carriers in contemporary biology is ferredoxin (Fd). Its fourfold cysteine-coordinated [2Fe-2S] core mediates electron transfer from photosystem I to ferredoxin-NADP ϩ -oxidoreductase, which reduces NADP ϩ to NADPH. A particularly interesting system is Fd from cyanobacterium Anabaena PCC7119 whose crystal structure was recently obtained at 1.3 and 1.17 Å resolution in the oxidized and the reduced forms (5), respectively. Most interestingly, it was found that two alternative conformations of Cys-46 exist, which is one of the four cysteinyl ligands of the [2Fe-2S] cluster (5). In the oxidized state Cys-46 adopts the so-called CO-in conformation, where the peptide oxygen points in the direction of the cluster, whereas, on reduction, the backbone flips to the CO-out conformation.Spin Coupling in Iron-Sulfur Clusters. In the ground state of the oxidized form of bioinorganic [mFe-nS] clusters, the Fe 3ϩ metal centers are typically in a local high-spin d 5 configuration [i.e., S Fe ϭ 5/2 for ferric Fe(III) centers], whereas they themselves are antiferromagnetically coupled to yield an overall low-spin state due to dominant superexchange interactions (6). In particular, the electronic ground state of [2Fe-2S] clusters in Fd has genuine multireference character and makes computational ...

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“…(53). In the case of the energetically more efficient spin-symmetry breaking there is also significant evidence for possible chemical or physical implications, as was shown for example by Yamaguchi,Fueno,and collaborators (43,54) in their classification of organic reaction mechanisms into the bi-radicaloid and non-radicaloid types. Finally, the symmetry breaking is of great importance for the electronic structure of extended systems, particularly for the organic polymers with conjugated double bonds.…”

Section: Introductionmentioning

confidence: 84%

Hartree–Fock stability and symmetry breaking: oxygen doubly negative ion

Paldus¹,

Čı́žek²

1985

Can. J. Chem.

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The Hartree-Fock stability problem, its relationship to the broken symmetry solutions, and the implications for a molecular nuclear framework distortion are briefly reviewed. The case where no nuclear framework distortion is possible is studied for the oxygen doubly negative ion, using an ab itzitio Slater-type orbital analytical approach, in order to illustrate other possible implications of the symmetry breaking in the independent particle models. It is shown that the existing pure singlet broken symmetry solutions for this ten electron ion, which were obtained earlier by ad hoc procedures, follows systematically and straightforwardly from the HF stability problem for the corresponding symmetry adapted solution which shows a strong singlet instability. The chemical and physical implications of this type of symmetry breaking are briefly discussed.Can. J. Chem. 63, 1803 ((985). On passe brikvement en revue le problkme de la stabilitC des solutions des equations de Hartree-Fock. On a mis en evidence le rble des solutions de symktrie brisCe et les implications par rapport une distorsion du squelette nucliaire moleculaire. Dans le but d'illustrer d'autres implications possibles du bris de symktrie dans le modkle a particules independantes, on a utilisk une approche analytique ab irritio avec des orbitales du type de Slater pour Ctudier l'ion doublement nCgatif de I'oxygene, un cas ou il n'y a pas de possibilitC de distorsion du squelette nuclCaire. On dkmontre que, pour cet ion a dix Clectrons, les solutions de symCtrie brisCe correspondant ides singulets purs, qui ont Ctt obtenues antirieurement par des procCdures nrl hoc, dCcoulent systkmatiquement et d'une facon directe du problkme de la stabilitt HF. La solution correspondante adaptCe pour la symCtrie posskde une instabilitk forte du type singulet. On discute brievement des implications chimiques et physiques de ce type de bris de symCtrie.[Traduit par le journal]

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Extended Hartree-Fock (EHF) theory in chemical reactions

Cited by 75 publications

References 28 publications

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Dynamical magnetostructural properties of Anabaena ferredoxin

Hartree–Fock stability and symmetry breaking: oxygen doubly negative ion

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Extended Hartree-Fock (EHF) theory in chemical reactions

Cited by 75 publications

References 28 publications

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Dynamical magnetostructural properties of Anabaena ferredoxin

Hartree–Fock stability and symmetry breaking: oxygen doubly negative ion

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Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)

Analytical and ab initio studies of effective exchange interactions, polyradical character, unpaired electron density, and information entropy in radical clusters (R)_N: Allyl radical cluster (N=2–10) and hydrogen radical cluster (N=50)