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  • 1
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of different CI basis sets, including doubly excited configurations, on transition energies calculated by modified CNDO and INDO methods is examined for H2O, NH3, CH4, and H2CO.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 22 (1971), S. 325-329 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Ergebnisse semiempirischer MO-CI-Rechnungen vom INDO- und RCNDO-Typ für die Elektronenspektren einiger Amine, des Fluormethans und einiger Perfluoralkane werden mitgeteilt. Für die größte Zahl der Moleküle können die niedrigeren elektronischen Übergänge gedeutet werden.
    Abstract: Résumé On présente les résultats de calculs semi-empiriques MO-CI du type INDO et RCNDO pour les spectres électroniques de quelques amines, les fluorométhanes, et quelques alcanes perfluorées. Des attributions raisonnables sont données pour les bandes électroniques de plus basse énergie dans la plupart des cas.
    Notes: Abstract Results of semi-empirical MO-CI calculations of the INDO and RCNDO type are presented for the electronic spectra of some amines, the fluoromethanes, and some perfluoroalkanes. Reasonable assignments for the lower electronic bands are found in the large majority of cases.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 22 (1971), S. 330-336 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die Ergebnisse semiempirischer Allvalenzelektronen-MO-CI-Rechnungen für die Elektronenspektren von Äthylen, Fluoräthylen, sowie einer Reihe von Iminen und Aldehyden werden mitgeteilt und mit den experimentellen Spektren verglichen.
    Abstract: Résumé Des calculs semi-empiriques tenant compte de tous les électrons de valence relatifs aux spectres électroniques de l'éthylène, des fluoroéthylènes, d'une série d'imines, et d'une série d'aldéhydes ont été effectués. On compare ces résultats aux spectres observés.
    Notes: Abstract Results of semi-empirical all-valence-electron MO-CI calculations are presented for the electronic spectra of ethylene, the fluoroethylenes, a series of imines, and a series of aldehydes. These results are compared with the experimental spectra.
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  • 4
    ISSN: 0040-5744
    Keywords: Key words: Symmetry breaking ; Correlation ; DFI ; HF instabilities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The solution of both Hartree–Fock (HF) and Kohn–Sham (KS) equations is based on the variational principle. Exact wavefunctions would obey the same symmetry restrictions contained in the total hamiltonian. However, the variational principle does not guarantee these symmetry restrictions and the HF and KS solutions are not necessarily symmetric in spin and space. Spatial and spin symmetry broken solutions with lower energies than their restricted analogues are examined for C2 and Be2, in the context of the KS formalism. Comparison with UHF solutions shows that KS instabilities are far less pronounced. The main differences between HF and KS solutions are related to effects of electron correlation.
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  • 5
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 6
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9546-9556 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Density functional calculations have been performed for small copper clusters, Cun (n≤5), using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. The calculations were of the all-electron type and local and nonlocal functionals were used. For each case, of both neutral and charged systems, several isomers have been considered in order to determine the lowest energy structures. The Jahn–Teller effect in Cu3 and Cu4 has been examined in detail. Bond lengths, equilibrium geometries, harmonic frequencies, adiabatic and vertical ionization potentials, adiabatic electron affinities, and binding energies are in reasonable agreement with experimental data, as well as with other theoretical results. © 1996 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 990-1002 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new quantum Monte Carlo (QMC) method of evaluating low lying vibrational levels for coupled modes is presented. We use a modified fixed-node (FN) approach in which an extremum principle for energy levels is invoked. In this way, the nodal hypersurfaces of the nuclear wave function are parametrized and then optimized for each excited state. The method is tested on the fundamental excitations of some two-dimensional model potentials and is applied to the case of realistic coupled modes of the CO molecule adsorbed on a palladium cluster. The effect of an external electric field is also examined. The quantum Monte Carlo results are compared with those obtained in the conventional variational treatment of the nuclear Schrödinger equation for coupled vibrations. The QMC results give the exact values with an error which is in general less than 1 cm−1 . In all cases (even in the case of strong coupling) the use of our procedure leads to "optimal'' nodal lines (in the sense of the extremum principle used in this work) which are practically undistorted. A salient feature of the Monte Carlo method presented here is that it readily permits the evaluation of the fundamental excitations of an arbitrary number of coupled vibrations. Furthermore, the potential energy surface may be represented by any analytical form without practical difficulties.
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  • 9
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Rechnungen vom Typ CNDO, INDO und RCNDO (CNDO mit höheren (Rydberg) Atomorbitalen in der Basis) unter Einschluß von Konfigurationswechselwirkung 1. Ordnung wurden für unverzweigte und verzweigte gesättigte Kohlenwasserstoffe durchgeführt. Die Resultate lassen eine Deutung der Hauptcharakteristika der beobachteten Elektronen-spektren zu. Die Wichtigkeit der äußeren Atomorbitale ist zu betonen. Die ersten Singulett-Singulett-Übergänge der stark verzweigten Paraffine führen zu angeregten Zuständen mit beträchtlichem „Rydbergcharakter“.
    Abstract: Résumé Des calculs CNDO, INDO et RCNDO (ayant des orbitales atomiques supérieures dans la base) ont été effectués sur les paraffines normales et ramifiées tenant compte de l'intéraction de configuration de premier ordre jusqu'à 30 configurations. Les résultats interprêtent d'une manière raisonnable les spectres électroniques mesurés. L'importance des orbitales atomiques supérieures apparaît clairement. La première bande observée des hydrocarbures hautement ramifiés comme le néopentane ou l'isobutane est attribuée à une transition dont l'état excité possède un fort caractère Rydberg.
    Notes: Abstract CNDO, INDO and RCNDO (CNDO including higher (Rydberg) atomic orbitals in the basis) calculations completed by first order configuration interaction were performed on straight chain and branched chain paraffins. The results interpret reasonably the main characteristics of the observed electronic spectra. The importance of outer atomic orbitals is stressed and it is found that the first singlet-singlet transition of highly branched paraffins leads to an excited state with considerable Rydberg character.
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  • 10
    ISSN: 1432-2234
    Keywords: Symmetry breaking ; Correlation ; DFI-HF instabilities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The solution of both Hartree-Fock (HF) and Kohn-Sham (KS) equations is based on the variational principle. Exact wavefunctions would obey the same symmetry restrictions contained in the total hamiltonian. However, the variational principle does not guarantee these symmetry restrictions and the HF and KS solutions are not necessarily symmetric in spin and space. Spatial and spin symmetry broken solutions with lower energies than their restricted analogues are examined for C2 and Be2, in the context of the KS formalism. Comparison with UHF solutions shows that KS instabilities are far less pronounced. The main differences between HF and KS solutions are related to effects of electron correlation.
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