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  • 1
    ISSN: 1572-8951
    Keywords: (Hyper)polarizabilities ; polymethines ; ground state ; excited singlet and triplet states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The electronic higher-order polarizabilities of linear and cyclic polymethine systems withelectron donor and acceptor groups included in the conjugation systems, in the ground and first excited singlet and triplet states, are studied using semiempirical quantum-chemical calculations (MNDO and PPP-DCI). It is shown that these polarizabilities are determined by two main factors: the bond order alternation in the conjugated system and the magnitude of the electron transfer within the molecule. The effect oftrans-cis isomerisation of the linear polymethines is also studied.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular engineering 8 (1998), S. 217-234 
    ISSN: 1572-8951
    Keywords: Density functional theory ; molecular hyperpolarizabilities ; relative accuracies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Recent density functional theory calculations of molecular hyperpolarizabilities are reviewed in order to try to assess the accuracy and reliability of DFT in the specified field by comparison with experiment and with ab initio HF and post-HF methods. In a table [1] (p. 157) containing results from the paper defining the compound electronic structure method Gaussian 2 [2], Foresman presents the relative accuracies of various 'model chemistries' for calculating thermochemical quantities. The Mean Absolute Deviation (MAD) from experiment, its Standard Deviation, and the largest positive and negative errors in the computed values, are the statistical means that allow the various models to be arranged in order of increasing MAD, and thus decreasing overall accuracy. These same statistical quantities, on a percent basis for size consistency and dimensionlessness, are used in this communication for quantifying the accuracies of various combinations of DFT functionals/basis sets/quantum chemical techniques/applied field strengths, in calculations of molecular mean dipole polarizabilities 〈α〉, first-order hyperpolarizabilities β∥ and second-order hyperpolarizabilities γ∥. The relative accuracies of DFT model chemistries are thus surveyed in three tables (including authors/references arranged in chronological order, compounds studied, and program codes employed), and can serve as guidelines for selecting optimal computational methodologies.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-8951
    Keywords: Polarizabilities ; pyrazolones ; hydroxypyrazoles ; tautomerism ; electronic structure ; excited states ; nonlinear optics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The (hyper)polarizabilities of different tautomer forms of hydroxypyrazoles and pyrazolones have been calculated by the finite-field procedure in the MNDO approximation and the sum of states formalism in the PPP approximation, with all singly- and doubly-excited electronic configurations in the CI method. It was shown that while in the ground electronic state the values of the (hyper) polarizabilities are not essentially different, in the first excited singlet Franck-Condon state an increase of the molecular polarizabilities of some tautomers is observed. This increase is attributed to a specific change in the electronic structure of the excited state, demonstrated by the localization of the electronic transition in the different pyrazolone tautomers. The electron-donor capabilities of phenyl-substituted hydroxypyrazoles and pyrazolones are discussed.
    Type of Medium: Electronic Resource
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