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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 27 (1972), S. 109-119 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Résumé Les orbitales moléculaires localisées sur les liaisons C-H de la molécule de méthane sont construites avec une ou deux orbitales gaussiennes sphériques optimisées en position et en grandeur. Lorsque deux orbitales gaussiennes sont utilisées, un problème de pseudodépendance des paramètres optimisés apparaît; l'introduction de contraintes dans le processus variationnel est alors étudiée. Pour les deux bases envisagées, les valeurs calculées de la longueur de la liaison C-H et de la constante de force pour le mode de vibration totalement symétrique de la molécule sont en bon accord avec l'expérience; des courbes d'isodensité électronique sont également présentées.
    Abstract: Zusammenfassung Mittels ein oder zwei optimalisierten Kugelgaußfunktionen werden lokalisierte MOs für die C-H-Bindungen des Methans konstruiert. Weil im Falle zweier Gaußfunktionen Pseudoabhängigkeit auftritt, wird die Einführung von Zusatzbedingungen in den Variationsprozeß untersucht. Bei beiden Basen sind die berechneten Werte für Bindungslänge und symmetrische Streckschwingung in guter Übereinstimmung mit dem Experiment.
    Notes: Abstract Molecular orbitals localized on the C-H bonds of the methane molecule are constructed by using one or two optimized spherical gaussian orbitals. If two gaussian orbitals are used, a problem of pseudodependence appears; consequently, we examine the introduction of constraints into the variational process. For the two bases we consider, the computed values of bond-length and force constant for the “breathing” vibrational mode are in good agreement with the experimental results; electronic isodensity curves are also presented.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 15 (2001), S. 215-219 
    ISSN: 1434-6079
    Keywords: PACS. 33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance) – 33.80.Gj Diffuse spectra; predissociation, photodissociation – 34.30.+h Intramolecular energy transfer; intramolecular dynamics; dynamics of van der Waals molecules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The wave operator theory of quantum dynamics is applied to characterize coupled metastable states. The theory extends to quasi bound states methods which are standard for dealing with bound levels. It is shown that interacting resonances can be investigated by means of small-dimensional effective Hamiltonians containing all the significant information of intrinsic properties which drive the various dynamical processes taking place. The study of the vibrational predissociation of I2Ne, mediated by intramolecular energy redistribution, illustrates the power of the method. In addition to its accuracy to determine spectroscopic profiles and survival probabilities, it results more efficient than usual energy or time-domain numerical calculations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 915-935 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Theoretical core effective potential methods are widely used in valence-only electron molecular calculations. These methods, which imply the frozen-core approximation, work well for the elements of the righthand side of the periodic table but are often unrealistic for metallic elements with highly polarizable cores. For these atoms one has to consider the polarization of the cores under the influence of the electric field created by the valence electrons. Moreover, relativistic corrections must be added for heavy atoms.Various theoretical approaches of core-valence interactions (polarization and core-valence correlations) will be reviewed, with a special emphasis on practical methods of calculation. The problem of handling the relativistic effects will mainly be discussed within the two-component Pauli formalism. It will be shown that the Foldy-Wouthuysen transformation is not the unique way for deriving relativistic corrections and that the second-order Dirac equation also provides a good starting point for obtaining relativistic corrections. Analytical exact results are given for the hydrogen atom. The accuracy of this approach is tested on many-electron atoms and molecules.It is finally shown that the problem of the core-valence separation is relevant to the general methodology of effective Hamiltonians that seems to provide the best promising way for filling the gap between the semiempirical and purely theoretical ab initio methods.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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