Limitations of density functional theory in application to degenerate states

Берсукер, И. Б.

doi:10.1002/(sici)1096-987x(19970130)18:2<260::aid-jcc10>3.0.co;2-m

Cited by 66 publications

(41 citation statements)

References 21 publications

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“…Density functional theory (DFT) is the modern alternative to the wavefunction-based ab initio methods. Although it is the most common theoretical method in quantum chemistry, up to now DFT is rarely used to discuss JT problems because of erroneous beliefs that it is not able to handle degenerate states [7]. Contrary to this, DFT can be applied to both degenerate and excited states, as formally proved by reformulation of the original Hohenberg-Kohn theorems-constrained search method and finite-temperature DFT [8].…”

Section: Introductionmentioning

confidence: 99%

Density functional theory study of the Jahn-Teller effect in cobaltocene

Zlatar

Schläpfer

Fowe

et al. 2009

Pure and Applied Chemistry

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A detailed discussion of the potential energy surface of bis(cyclopentadienyl)cobalt(II), cobaltocene, is given. Vibronic coupling coefficients are calculated using density functional theory (DFT). Results are in good agreement with experimental findings. On the basis of our calculation, there is no second-order Jahn-Teller (JT) effect as predicted by group theory. The JT distortion can be expressed as a linear combination of all totally symmetric normal modes of the low-symmetry, minimum-energy conformation. The out-ofplane ring deformation is the most important mode. The JT distortion is analyzed by seeking the path of minimal energy of the adiabatic potential energy surface.

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Section: Introductionmentioning

confidence: 99%

Density functional theory study of the Jahn-Teller effect in cobaltocene

Zlatar

Schläpfer

Fowe

et al. 2009

Pure and Applied Chemistry

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“…If the value of k(ET) is equal or close to κ ≈ 1, the ET is adiabatic, and if κ <<< 1, it is non-adiabatic [21]. For non-adiabatic ET the DFT calculation of the electronic structure of the substrate is not valid and no conclusion regarding the reactivity of the substrate ions can be made [22,23]. More sophisticated electronic structure methods, like MCSCF must be applied to these studied processes [22,24,25].…”

Section: Resultsmentioning

confidence: 99%

Disposal of Poisonous Organic Halides by Using the Electrochemical Method: DFT Simulation

Spataru¹,

Fernández²,

Sista³

et al. 2016

ChemJMold

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Abstract. Geometry optimizations at the UBP86/6-311++G** level of electronic structure theory have been performed for DDT, β-hexachlorocyclohexane, and heptachlor organic polychlorides as well for their positive and negative ions. The HOMO composition of these neutral molecules show no participation of the carbon-chlorine atomic orbitals, while LUMO of the calculated molecules include a major contribution of the anti-bonding character atomic orbitals from the two or three carbon-chloride bonds of each calculated molecule. Consequently, the negative ions were the most sensitive structure during the geometry optimization, showing the carbon-chloride bonds cleaving during the electronic structure calculations. Further geometry optimization of the obtained neutral intermediate molecules after the fi rst and second reducing by two electrons show that the electrochemical dehalogenation of the organic poychlorides is sequential.Keywords: poisonous pesticides, organic chlorides, electrochemistry, DFT, carbon-chloride bonds. IntroductionThe electrochemical method for disposal of halogenated organic compounds leads to complete mineralization of organic halides. Generally, the electro-reductive treatments using new, improved electrochemical sensors, lead to partial recovery/recycling of chemicals, are regarded as an advantageous [1]. Methods of chemical and electro-chemical oxidation applied to organic pollutants attain, in most cases, a complete mineralization, being considered to have highenergy requirements [2]. Reduction will not lead to a complete mineralization, but to a complete dehalogenation, with a possible formation of double bonds. This has been proven for organic halides with one [3,4], two [5,6], three [7], four [8] or six [9] halogen atoms in their structure.Dehalogenation reactions of halogen-alkanes have been studied by direct and indirect electrochemical reductions and classical kinetics. The electrochemical redox processes can be divided into two categories: direct (heterogeneous) and indirect or mediated (homogeneous) ones. Direct electrochemical reduction involves electrons accepted directly by the analyte from the cathode surface, while indirect electrochemical reduction occurs between the analyte and an electrogenerated species, which serves as catalyst. Some authors use the term "mediator" as an alternative for catalyst [1]. The catalyst can exist in the electrolyte solution or can be immobilized on the electrode surface, namely CME's or chemically modifi ed electrodes [1,10]. By modifying the surface of the electrodes by adsorption of molecules or ions, the surface reactivity and slow kinetics can be overcome [10].Mechanistically, the halogen atoms are removed in a successive fashion, along with a two electron transfer at more and more cathodic (negative) potentials. This has been proven for polyhalogenated aromatics [11] and remains under question for polyhalogenated aliphatics. The diffi culty of attaining suffi ciently cathodic potentials would explain why complete dehalogenation does not alway...

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“…On the other hand, our recent electron structure studies show that the HOMO-LUMO and Co-C σ-σ * MO gaps are signifi cantly smaller in the Co(II) methylcobalamin system compared with Co(III) methylcobalamin, proving that the orbital mixing is effective [106]. Therefore, the activation of Co-C bond cleavage in cobalamin bio-chemistry must be treated as an orbital mixing process and the Co(II) methylcobalamin system cannot be treated c orrectly by DFT methods [107], as it is a Pseudo-Jahn-Teller system [108]. Such orbital mixing leads to a fractional population of the σ and σ * orbitals, including also several bonding occupied and antibonding unoccupied orbitals [106].…”

Section: The Multi-confi Guration Effects In Methylcob(ii)alamin and mentioning

confidence: 99%

The Nature of the Co-C Bond Cleavage Processes in Methylcob(II)Alamin and Adenosylcob(III)Alamin

Spataru¹,

Fernández²

2016

ChemJMold

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Abstract. Unfortunately, there are still signifi cant disagreements between experimental and theoretical data of rate constants, energy barriers for Co-C bond cleavage process and coordination numbers of vitamin B 12 coenzyme species in spite of the remarkable efforts done by research community. Therefore, no grounded mechanisms for Co-C vitamin B 12 coenzyme bond breaking process and subsequent reactions have been found up to now. The infl uence of the mixing orbitals e.g. Pseudo-Jahn-Teller and similar effects on the reactions paths of bond-cleavage mechanisms of vitamin B 12 co-factors must be taken into account by utilizing multi-reference methods, in particular multiconfi gurational self-consistent fi eld (MCSCF) method. Then, the change in total energy along the normal coordinate Q for the stretching mode including Co-C and Co-N bonds in vitamin B 12 cofactors is expected due to a "vibronic" coupling term, which couples an excited state and ground state by a second order derivative potential-energy operator. The strong state mixing effect is expected to lead to low energy barriers and to Co-C and Co-N axial bond cleavage events in agreement with experimental data. Afterward, the updated mechanisms of vitamin B 12 bio-processes can be determined.Keywords: vitamin B 12 , mechanism, bio-catalysis, Pseudo-Jahn-Teller effect, DFT, MCSCF. Received: December 2015/ Revised fi nal: February 2016/ Accepted: February 2016 IntroductionVitamin B 12 cofactor is one of eight B vitamins and is involved in mammalian cellular metabolism, infl uencing amino acid and DNA synthesis [1] and hematopoiesis. The best known human physiological function of vitamin B 12 is its role in promoting normal health in the brain and nervous system. Vitamin B 12 anemia can cause such neurologic dysfunction as weakness, fatigue, light-headedness, rapid heartbeat, rapid breathing, pale skin color, bruising, and bleeding (including bleeding gums). The more severe vitamin B 12 anemia dysfunctions are characterized by tingling or numbness of the fi ngers and toes, diffi culty walking, mood changes, depression, memory loss, disorientation and, in most severe cases, dementia [2]. Vitamin B 12 defi ciency has even been considered in playing a role in the development of Alzheimer's disease [3][4][5][6][7].The vitamin B 12 cofactor contains a cobalt atom surrounded by an equatorial corrin ring. Covalently linked to the central atom is a dimethylbenzimidazole that occupies one of the axial coordination positions. The opposite coordinate is available for several ligands in bio-medium or in solution; however, known biologically active structures containing adenosyl-or methyl have been considered most often (Figure 1).

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Limitations of density functional theory in application to degenerate states

Cited by 66 publications

References 21 publications

Density functional theory study of the Jahn-Teller effect in cobaltocene

Density functional theory study of the Jahn-Teller effect in cobaltocene

Disposal of Poisonous Organic Halides by Using the Electrochemical Method: DFT Simulation

The Nature of the Co-C Bond Cleavage Processes in Methylcob(II)Alamin and Adenosylcob(III)Alamin

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