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Jean-paul Malrieu - One of the best experts on this subject based on the ideXlab platform.

  • Aromaticity: an ab Initio Evaluation of the Properly Cyclic Delocalization Energy and the π-Delocalization Energy Distortivity of Benzene
    The journal of physical chemistry. A, 2008
    Co-Authors: Celestino Angeli, Jean-paul Malrieu
    Abstract:

    A complete active space self-consistent field (CASSCF) calculation of the π system of a conjugated molecule enables one to define optimal valence π and π* molecular orbitals (MOs). One may define from them a set of atom-centered orthogonal π orbitals, one per carbon atom, and the resulting upper multiplet is used to define the π-electron Delocalization Energy. This quantity is confirmed to be slightly distortive, i.e., to prefer bond-alternated geometries. One may also define strongly localized bond MOs corresponding to a Kekule structure and then perturb the associated strongly localized single determinant under the effect of the Delocalization between the bonds and of the electronic correlation. The third order of perturbation introduces the contribution of the cyclic circulation of the electrons around the benzene ring, i.e. the aromatic Energy contribution. Its value is about 1.5 eV. It is antidistortive, but remains important under bond alternation. The cyclic correlation effects are of minor importance.

  • Aromaticity : an ab Initio Evaluation of the Properly Cyclic Delocalization Energy and the π-Delocalization Energy Distortivity of Benzene
    Journal of Physical Chemistry A, 2008
    Co-Authors: Celestino Angeli, Jean-paul Malrieu
    Abstract:

    A complete active space self-consistent field (CASSCF) calculation of the π system of a conjugated molecule enables one to define optimal valence π and π* molecular orbitals (MOs). One may define from them a set of atom-centered orthogonal π orbitals, one per carbon atom, and the resulting upper multiplet is used to define the π-electron Delocalization Energy. This quantity is confirmed to be slightly distortive, i.e., to prefer bond-alternated geometries. One may also define strongly localized bond MOs corresponding to a Kekulé structure and then perturb the associated strongly localized single determinant under the effect of the Delocalization between the bonds and of the electronic correlation. The third order of perturbation introduces the contribution of the cyclic circulation of the electrons around the benzene ring, i.e. the aromatic Energy contribution. Its value is about 1.5 eV. It is antidistortive, but remains important under bond alternation. The cyclic correlation effects are of minor importance.

  • Evaluating the cyclic π-electron Delocalization Energy through a double cut of conjugated rings
    New Journal of Chemistry, 2007
    Co-Authors: Jean-paul Malrieu, Christine Lepetit, Mickaël Gicquel, Jean-louis Heully, Patrick W. Fowler, Remi Chauvin
    Abstract:

    The cutting of two bonds of a ring AB allows us to define two closed-shell disconnected fragments A and B, and to evaluate the Energy of the AB molecule from the eigenstates of A and B by second-order perturbation theory in the framework of tight-binding/Huckel theory. Diagrammatic arguments allow identification of the properly cyclic π-electron Delocalization contribution to the Energy, which we denote ecyc(AB), and which can be simply expressed in terms of the energies of the cyclic molecule, its fragments and of the two singly bridged and systems. The rules for the selection of suitable A and B fragments are given. The mathematical expression for ecyc(AB) can be translated into a chemical scheme that defines a new energetic aromaticity index, referred to as aromatic cyclic Energy (ACE), which may be simply calculated from five Huckel energies. ACE of neutral and ionic [N]annulenes and their ring carbo-mers have been estimated, and shown to yield consistent evaluations of aromatic and antiaromatic cyclic energetic effects. A comparison is made with two other indices of aromaticity, Breslow resonance energies and ELFπ values.

  • The instantaneous image effect: A novel contribution to the mechanism of heterogeneous catalysis
    Catalysis Letters, 1991
    Co-Authors: Jean-paul Malrieu, Lionel Salem
    Abstract:

    A novel contribution to the mechanism of heterogeneous catalysis is discussed for a model H2-on-nickel (100) system. The effect, which corresponds in a first approximation to the dispersion Energy between adsorbate molecule and metal, is calculated through (1) admixture of an ionic component in the wave function of the adsorbate; (2) interaction between this ionic component and the image dipole which it creates in the polarizable metal. A single VB model, using an Anderson-type evaluation of the Delocalization Energy between adsorbate and metal, shows the image contribution to be 10 to 15% of the total adsorbate ↔ metal interaction Energy.

Celestino Angeli - One of the best experts on this subject based on the ideXlab platform.

  • Aromaticity: an ab Initio Evaluation of the Properly Cyclic Delocalization Energy and the π-Delocalization Energy Distortivity of Benzene
    The journal of physical chemistry. A, 2008
    Co-Authors: Celestino Angeli, Jean-paul Malrieu
    Abstract:

    A complete active space self-consistent field (CASSCF) calculation of the π system of a conjugated molecule enables one to define optimal valence π and π* molecular orbitals (MOs). One may define from them a set of atom-centered orthogonal π orbitals, one per carbon atom, and the resulting upper multiplet is used to define the π-electron Delocalization Energy. This quantity is confirmed to be slightly distortive, i.e., to prefer bond-alternated geometries. One may also define strongly localized bond MOs corresponding to a Kekule structure and then perturb the associated strongly localized single determinant under the effect of the Delocalization between the bonds and of the electronic correlation. The third order of perturbation introduces the contribution of the cyclic circulation of the electrons around the benzene ring, i.e. the aromatic Energy contribution. Its value is about 1.5 eV. It is antidistortive, but remains important under bond alternation. The cyclic correlation effects are of minor importance.

  • Aromaticity : an ab Initio Evaluation of the Properly Cyclic Delocalization Energy and the π-Delocalization Energy Distortivity of Benzene
    Journal of Physical Chemistry A, 2008
    Co-Authors: Celestino Angeli, Jean-paul Malrieu
    Abstract:

    A complete active space self-consistent field (CASSCF) calculation of the π system of a conjugated molecule enables one to define optimal valence π and π* molecular orbitals (MOs). One may define from them a set of atom-centered orthogonal π orbitals, one per carbon atom, and the resulting upper multiplet is used to define the π-electron Delocalization Energy. This quantity is confirmed to be slightly distortive, i.e., to prefer bond-alternated geometries. One may also define strongly localized bond MOs corresponding to a Kekulé structure and then perturb the associated strongly localized single determinant under the effect of the Delocalization between the bonds and of the electronic correlation. The third order of perturbation introduces the contribution of the cyclic circulation of the electrons around the benzene ring, i.e. the aromatic Energy contribution. Its value is about 1.5 eV. It is antidistortive, but remains important under bond alternation. The cyclic correlation effects are of minor importance.

Remi Chauvin - One of the best experts on this subject based on the ideXlab platform.

  • Evaluating the cyclic π-electron Delocalization Energy through a double cut of conjugated rings
    New Journal of Chemistry, 2007
    Co-Authors: Jean-paul Malrieu, Christine Lepetit, Mickaël Gicquel, Jean-louis Heully, Patrick W. Fowler, Remi Chauvin
    Abstract:

    The cutting of two bonds of a ring AB allows us to define two closed-shell disconnected fragments A and B, and to evaluate the Energy of the AB molecule from the eigenstates of A and B by second-order perturbation theory in the framework of tight-binding/Huckel theory. Diagrammatic arguments allow identification of the properly cyclic π-electron Delocalization contribution to the Energy, which we denote ecyc(AB), and which can be simply expressed in terms of the energies of the cyclic molecule, its fragments and of the two singly bridged and systems. The rules for the selection of suitable A and B fragments are given. The mathematical expression for ecyc(AB) can be translated into a chemical scheme that defines a new energetic aromaticity index, referred to as aromatic cyclic Energy (ACE), which may be simply calculated from five Huckel energies. ACE of neutral and ionic [N]annulenes and their ring carbo-mers have been estimated, and shown to yield consistent evaluations of aromatic and antiaromatic cyclic energetic effects. A comparison is made with two other indices of aromaticity, Breslow resonance energies and ELFπ values.

D. S. Sanditov - One of the best experts on this subject based on the ideXlab platform.

  • Rationale for Introducing an Additional Term into the Glass Transition Criterion
    Inorganic Materials, 2020
    Co-Authors: D. S. Sanditov, S. S. Badmaev
    Abstract:

    — A modification to a previously proposed glass transition criterion is analyzed and substantiated in terms of the delocalized atom model. The atom Delocalization Energy in sodium germanate, alkali silicate, and sodium borate glasses is shown to be a linear function of their glass transition temperature.

  • Energy of Atom Delocalization and Thermal Motion in the Region of Vitrification
    Russian Physics Journal, 2019
    Co-Authors: D. S. Sanditov, M. V. Darmaev
    Abstract:

    A linear correlation has been established between the empirical parameter D of the Enkel equation for the viscosity and the vitrification temperature Tg of inorganic glasses, which is discussed within the framework of the model of delocalized atoms. From an analysis of this correlation, certain information on the vitrification and the viscous flow of glass-forming liquids follows. The value of D is an unambiguous function of the atom Delocalization Energy.

  • Delocalized-Atom Model and Properties of Sulfophosphate Glasses
    Inorganic Materials, 2019
    Co-Authors: D. S. Sanditov, S. S. Badmaev
    Abstract:

    — The basic concepts of the delocalized-atom model have been shown to be applicable to low-melting-point sulfophosphate glasses and parameters of the model have been calculated. The parameters have been used to gain insight into the “atom Delocalization” process in the glasses and assess their properties (viscosity, microhardness, glass transition temperature, and internal pressure). The results demonstrate that there is a linear correlation between the atom Delocalization Energy and glass transition temperature. The melt–glass transition is accompanied by the freezing of the atom Delocalization process.

  • Delocalization Energy of atoms in inorganic glass
    Glass Physics and Chemistry, 2016
    Co-Authors: D. S. Sanditov, M. V. Darmaev, A. A. Mashanov
    Abstract:

    For multicomponent sheet and lead glass, the Delocalization Energy of Δe e atoms is calculated from the experimental data on viscosity. It is shown that the value of Δe e remains constant in sufficiently broad temperature range in the glass transition region. The results are in good agreement with the calculation on the formula of the model of delocalized atoms, which includes the glass transition temperature and fraction of fluctuating volume frozen at this temperature.

  • Delocalization Energy of atoms in inorganic glass
    Glass Physics and Chemistry, 2016
    Co-Authors: D. S. Sanditov, M. V. Darmaev, A. A. Mashanov
    Abstract:

    For multicomponent sheet and lead glass, the Delocalization Energy of Δε_ e atoms is calculated from the experimental data on viscosity. It is shown that the value of Δε_ e remains constant in sufficiently broad temperature range in the glass transition region. The results are in good agreement with the calculation on the formula of the model of delocalized atoms, which includes the glass transition temperature and fraction of fluctuating volume frozen at this temperature.

Karl Jug - One of the best experts on this subject based on the ideXlab platform.

  • Delocalization Energy of .pi. Electrons as an Index for Aromaticity of Polycyclic Hydrocarbons
    The Journal of Organic Chemistry, 1994
    Co-Authors: Sabine Behrens, Andreas M. Koester, Karl Jug
    Abstract:

    SINDOI calculations of an improved π electron Delocalization Energy with geometry optimization were performed for a large number of mono- and polycyclic hydrocarbon rings and compared with ab initio results. The suitability of the Delocalization Energy as aromaticity index is demonstrated. For a comparison of the aromaticity of molecules with different size and different number of rings, a normalized Delocalization Energy per broken π bond in the reference state was introduced. With this criterion the aromaticity of polycyclic conjugated hydrocarbons with four- and six-membered rings was examined and an energetic aromaticity scale established