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Theoretical Chemistry and Molecular Modelling

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  1. Momentum space analysis of the electronic structure of biphenyl

    MORINI, Filippo; SHOJAEIKOHNEHSHAHRI, Reza; DELEUZE, Michael
    The results of a yet to come experimental study of the electronic structure of biphenyl employing electron momentum spectroscopy (EMS) have been theoretically predicted, taking into account complications such as structural mobility in the electronic ground state, electronic correlation and relaxation, and a dispersion of the inner-valence ionization intensity to electronically excited (shake-up) configurations in the cation. The main purpose of this work is to explore the current limits of EMS in unraveling details of the molecular structure, namely the torsional characteristics of large and floppy aromatic molecules. At the benchmark ADC(3)/cc-pVDZ level of theory, the influence of the twist...

  2. Quantum chemical and kinetic study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals. II. The H abstraction pathway

    SHIROUDI, Abolfazl; DELEUZE, Michael
    Reaction mechanisms for the initial stages of naphthalene oxidation at high temperatures (T> 600 K) have been studied theoretically using density functional theory along with various exchange-correlation functionals, as well as the benchmark CBS-QB3 quantum chemical approach. These stages correspond to the removal of hydrogen atoms by hydroxyl radical and the formation thereby of 1- and 2-naphthyl radicals. The oxidation mechanisms of naphthalene by OH radicals under inert (He) conditions and at temperatures larger than 600 K have been studied using Density Functional Theory (DFT) along with various exchange-correlation functionals. Comparison is made with benchmark CBS-QB3 theoretical results. Kinetic rate...

  3. Quantum chemical and kinetic study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals. I. The OH addition pathway

    SHIROUDI, Abolfazl; DELEUZE, Michael; Canneaux, Sébastien
    The oxidation mechanisms of naphthalene by OH radicals under inert (He) conditions and at temperatures smaller than 410 K have been studied [1] using Density Functional Theory along with various exchange-correlation functionals. Comparison is made with benchmark CBS-QB3 theoretical results. Kinetic rate constants were estimated by means of Transition State Theory (TST) and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Effective rate constants have been calculated according to a steady state analysis using a two-step model. Comparison with experiment confirms that, on the OH addition reaction pathway leading to 1-naphthol, the first bimolecular reaction step has an effective negative activation energy around -1.5...

  4. Theoretical Study of the Oxidation Mechanisms of Naphthalene Initiated by Hydroxyl Radicals: The OH-Addition Pathway

    SHIROUDI, Abolfazl; Deleuze, Michael S.; Canneaux, Sébastien
    The oxidation mechanisms of naphthalene by OH radicals under inert (He)conditions have been studied using density functional theory along with various exchange−correlation functionals. Comparison has been made with benchmark CBS-QB3 theoretical results. Kinetic rate constants were correspondingly estimated by means of transition state theory and statistical Rice−Ramsperger−Kassel−Marcus (RRKM) theory. Comparison with experiment confirms that, on the OH-addition reaction pathway leading to 1-naphthol, the first bimolecular reaction step has an effective negative activation energy around −1.5 kcal mol−1, whereas this step is characterized by an activation energy around 1 kcal mol−1 on the OH-addition reaction pathway leading to 2-naphthol. Effective rate constants...

  5. Theoretical Chemistry in Belgium - A Topical Collection from Theoretical Chemistry Accounts


  6. Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals

    SHIROUDI, Abolfazl; Deleuze, Michael; MORINI, Filippo

  7. Theoretical Study of the Oxidation Mechanisms of Naphthalene Initiated by Hydroxyl Radicals: The H Abstraction Pathway

    SHIROUDI, Abolfazl; DELEUZE, Michael
    Reaction mechanisms for the initial stages of naphthalene oxidation at high temperatures (T ≥ 600 K) have been studied theoretically using density functional theory along with various exchange-correlation functionals, as well as the benchmark CBS-QB3 quantum chemical approach. These stages correspond to the removal of hydrogen atoms by hydroxyl radical and the formation thereby of 1- and 2-naphthyl radicals. Bimolecular kinetic rate constants were estimated by means of transition state theory. The excellent agreement with the available experimental kinetic rate constants demonstrates that a two step reaction scheme prevails. Comparison with results obtained with density functional theory in conjunction with...

  8. Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran (vol 417, pg 17, 2013)

    Shojaei, S.H.Reza; MORINI, Filippo; Deleuze, M. S.
    A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green???s Function calculations employing the outervalence Green???s Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning???s correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron p-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within 0.15 eV accuracy, up to the r-ionization onset. The lower ionization energy of carbazole is the combined result of mesomeric and...

  9. Erratum to ‘‘Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran’’ [Chem. Phys. 417 (2013) 17–25]

    Shojaei, S.H.Reza; MORINI, Filippo; Deleuze, M. S.

  10. Electron Momentum Spectroscopy of 1???Butene: A Theoretical Analysis Using Molecular Dynamics and Molecular Quantum Similarity

    Shojaei, S.H.Reza; Vandenbussche, Jelle; Deleuze, M. S.; Bultinck, Patrick
    The results of experimental studies of the valence electronic structure of 1-butene by means of electron momentum spectroscopy (EMS) have been reinterpreted on the basis of molecular dynamical simulations in conjunction with the classical MM3 force field. The computed atomic trajectories demonstrate the importance of thermally induced nuclear dynamics in the electronic neutral ground state, in the form of significant deviations from stationary points on the potential energy surface and considerable variations of the C???C???C???C dihedral angle. These motions are found to have a considerable influence on the computed spectral bands and outer-valence electron momentum distributions. Euclidean distances between spherically averaged electron momentum densities confirm that...

  11. Comparison of Geant4-DNA simulation of S-values with other Monte Carlo codes

    André, Thierry; MORINI, Filippo; Karamitros, M.; Delorme, R.; Le Loirec, C.; Campos, L.; Champion, C.; Groetz, J.-E.; Fromm, M.; Bordage, M.-C.; Perrot, Y.; Barberet, Ph.; Bernal, M.A.; Brown, J.M.C.; Deleuze, M. S.; Francis, Z.; Ivanchenko, V.; Mascialino, B.; Zacharatou, C.; Bardiès, M.; Incerti, S.
    Monte Carlo simulations of S-values have been carried out with the Geant4-DNA extension of the Geant4 toolkit. The S-values have been simulated for monoenergetic electrons with energies ranging from 0.1 keV up to 20 keV, in liquid water spheres (for four radii, chosen between 10 nm and 1 μm), and for electrons emitted by five isotopes of iodine (131, 132, 133, 134 and 135), in liquid water spheres of varying radius (from 15 μm up to 250 μm). The results have been compared to those obtained from other Monte Carlo codes and from other published data. The use of the...

  12. Theoretical chemistry in Belgium

    Champagne, Benoit; DELEUZE, Michael; De Proft, Frank; Leyssens, Tom
    Chemistry, Physical

  13. Half-metallicity of graphene nanoribbons and related systems: a new quantum mechanical El Dorado for nanotechnologies... or a hype for materials scientists?

    DELEUZE, Michael; HUZAK, Matija; HAJGATO, Balazs
    In this work we discuss in some computational and analytical details the issue of half-metallicity in zig-zag graphene nanoribbons and nanoislands of finite width, i.e. the coexistence of metallic nature for electrons with one spin orientation and insulating nature for the electrons of opposite spin, which has been recently predicted from so-called first-principle calculations employing Density Functional Theory. It is mathematically demonstrated and computationally verified that, within the framework of non-relativistic and time-independent quantum mechanics, like the size-extensive spin-contamination to which it relates, half-metallicity is nothing else than a methodological artefact, due to a too approximate treatment of electron correlation...

  14. Valence one-electron and shake-up ionization bands of fluorene, carbazole and dibenzofuran

    SHOJAEIKOHNEHSHAHRI, Reza; MORINI, Filippo; DELEUZE, Michael
    A comprehensive study of the He (I) ultra-violet photoelectron spectra of fluorene, carbazole and dibenzofuran is presented with the aid of one-particle Green's Function calculations employing the outervalence Green's Function (OVGF) approach and the third-order algebraic diagrammatic construction [ADC(3)] scheme, along with Dunning's correlation consistent basis sets of double and triple zeta quality (cc-pVDZ, cc-pVTZ). Extrapolations of the ADC(3) results for the outermost one-electron pi-ionization energies to the cc-pVTZ basis set enable theoretical insights into He (I) measurements within similar to 0.15 eV accuracy, up to the sigma-ionization onset. The lower ionization energy of carbazole is the combined result of...

  15. Photoelectron and Electron Momentum Spectroscopy of Tetrahydrofuran from a Molecular Dynamical Perspective

    Shojaei, S.H.Reza; Morini, Filippo; Deleuze, Michael S.
    The results of experimental studies of the valence electronic structure of tetrahydrofuran employing He I photo- electron spectroscopy as well as Electron Momentum Spectrosco- py (EMS) have been reinterpreted on the basis of Molecular Dynamical simulations employing the classical MM3 force ???eld and large-scale quantum mechanical simulations employing Born??? Oppenheimer Molecular Dynamics in conjunction with the dispersion corrected ??B97XD exchange-correlation functional. Analysis of the produced atomic trajectories demonstrates the importance of thermal deviations from the lowest energy path for pseudorotation, in the form of considerable variations of the ring- puckering amplitude. These deviations are found to have a signi???cant in???uence on several outer-valence electron momentum distributions, as well as on the He I...

  16. Benchmark theoretical study of the electric polarizabilities of naphthalene, anthracene and tetracene

    Huzak, M.; Deleuze, M. S.
    By applying the principles of a focal point analysis to finite field calculations, the static electric dipole polarizabilities of naphthalene, anthracene, and tetracene have been estimated up to the level of coupled cluster theory including single, double, and perturbative triple excitations in the limit of an asymptotically complete basis set. Thermal corrections to polarizabilities have been empirically estimated according to Born-Oppenheimer molecular dynamical simulations at 298 K employing density functional theory. Confrontation with the latest experimental values for isotropic polarizabilities ultimately indicates relative accuracies of the order of 1.2% (for naphthalene) to 3.5% (for anthracene), provided diffuse functions are incorporated...

  17. Quenching of magnetism in hexagonal graphene nanoflakes by non-local electron correlation

    HAJGATO, Balazs; DELEUZE, Michael
    Non-local MP2-like electron correlation in DFT calculations employing the double hybrid dispersion corrected B2PLYD functional is found to systematically quench anti-ferromagnetism in a variety of hexagonal graphene nanoflakes. The scaling in size of the associated spin contamination demonstrates further the artefactual character of any spin-polarization of electron densities in singlet electronic states.

  18. Benchmark theoretical study of the ionization energies, electron affinities and singlet-triplet energy gaps of azulene, phenanthrene, pyrene, chrysene and perylene

    HUZAK, Matija; HAJGATO, Balazs; DELEUZE, Michael
    The vertical and adiabatic singlet-triplet energy gaps, electron affinities and ionization energies of azulene, phenanthrene, pyrene, chrysene, and perylene are computed by applying the principles of a focal point analysis onto a series of single-point calculations at the level of Hartree-Fock theory, second-, third-, and fourth-order Moller-Plesset perturbation theory, as well as coupled cluster theory including single, double and perturbative triple excitations, in conjunction with correlation consistent basis sets of improving quality. Results are supplemented with an extrapolation to the limit of an asymptotically complete basis set. According to our best estimates, azulene, phenanthrene, pyrene, chrysene, and perylene exhibit adiabatic...

  19. Electron momentum spectroscopy of metal carbonyls: a reinvestigation of the role of nuclear dynamics

    Hajgato, Balazs; Morini, Filippo; Deleuze, Michael
    The main purpose of this work is to reinvestigate the influence of nuclear dynamics in the electronic ground state of group 6 metal hexacarbonyl compounds [W(CO)6, Cr(CO)6, Mo(CO)6] on electron momentum density profiles obtained from experimental orbital reconstructions employing Electron Momentum Spectroscopy. We call into questionthe view (Liu et al. in Chem Phys Lett 497:229, 2010) that thermally induced nuclear displacements associated with the first three triply degenerate 1T2g, 1T1u, and 1T2u vibrational eigenmodes can be large enough at or near room temperature (298–310K) to explain on their own the unexpectedly large electron densities inferred for the frontier orbitals of...

  20. The band 12 issue of norbornane: A study of higher shake-up states

    Knippenberg, Stefan; HAJGATO, Balazs
    In line with a recent study of the electronic structure of the cage compound norbornane (J. Chem. Phys. 121 (2004), 10525:J. Phys. Chem. A 109 (2005), 4267), symmetry adapted cluster expansion configuration interaction (SAC-CI) general R calculations have been performed and compared with results obtained by the third order algebraic diagrammatic construction scheme [ADC(3)]. Comparison has been made with previously performed electron momentum spectroscopy (EMS) and ultraviolet photo-electron measurements. The region around similar to 25eV (band 12), characterized by an elaborated band in the EMS spectrum which is missing in previous Green's function and ADC calculations, is investigated. This study...

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