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  • 1
    Electronic Resource
    Electronic Resource
    VB calculations with orthogonal basis functions (1978)
    Springer
    Theoretical chemistry accounts 47 (1978), S. 193-203 
    Details
    ISSN: 1432-2234
    Keywords: VB method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract As a first step in the development of a semiempirical VB method,ab initio VB calculations were performed to obtain potential energy curves for the molecules HF and BeH2 and the energy profile of the collinear exchange reaction F + H2 → HF + H. The applicability of the method is discussed with particular emphasis on the calculation of integrals over OAO's, the choice of valence structures to be included in the CI scheme and the interpretation of the wave function in terms of OAO's.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00577161
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular orbital calculations based on linear combinations of fragment orbitals (1978)
    Springer
    Theoretical chemistry accounts 49 (1978), S. 77-92 
    Details
    ISSN: 1432-2234
    Keywords: Photoelectron spectra, interpretation of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A semiempirical MO method based on localized fragment orbitals has been developed, which is particularly suited for the construction of orbital correlation diagrams for the discussion of the electronic structure of complex molecules in terms of fragments and their interactions. The method allows for the inclusion of experimental ionization potentials and electron affinities of the fragments within the calculation of the Fock matrix elements and may thus form the basis of an interpretation of photoelectron spectra, comparable to the interpretation of UV spectra by means of the MIM method of Longuet-Higgins and Murrell. Several levels of approximation are discussed using the acrolein molecule as an example.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00552740
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  • 3
    Electronic Resource
    Electronic Resource
    Pariser-Parr-Pople-Rechnungen an Molekülen mit Aminogruppen (1966)
    Springer
    Theoretical chemistry accounts 5 (1966), S. 236-250 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract PPP-calculations were performed for aniline with different sets of parameters for the amino group. Using δω N=−11.47 eV, β CN=−2.30 eV, γ 11 (N)=12.83 eV and two-centre-Coulomb integrals evaluated according to the procedure due to Mataga, the agreement between calculated and experimental data is excellent, for aniline as well as for the phenylene-diamines. Parameter values and results for the ground state and the lowest excited singlet states of aniline are discussed.
    Abstract: Résumé Des calculs PPP ont été effectués sur l'aniline avec différents jeux de paramètres pour le groupe amino. En utilisant δω N=−11,47 eV, β CN=−2,30 eV, γ 11 (N)=12,83 eV et des intégrales coulombiennes bi-centriques évaluées selon le procédé de Mataga, l'accord entre la théorie et l'expérience est excellent tant pour l'aniline que pour les phénylène diamines. On discute les valeurs des paramètres et les résultats pour l'état fondamental et le plus bas singulet excité de l'aniline.
    Notes: Zusammenfassung PPP-Rechnungen am Anilin wurden mit verschiedenen Parametern für die Aminograppe durchgeführt. Mit δω N=−11.47 eV, β CN=−2.30 eV, γ 11 (N)=12.83 eV und nach der von Mataga vorgeschlagenen Formel berechneten Zweizentren-Coulombintegralen erhält man für das Anilin und die Phenylendiamine eine sehr gute Übereinstimmung zwischen den berechneten und den experimentellen Daten. Die Wahl der Parameter sowie die Ergebnisse für den Grund-zustand und die ersten angeregten Singulettzustände werden diskutiert.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526937
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  • 4
    Electronic Resource
    Electronic Resource
    Ab initio and model hypersurfaces for ground and excited state radical reactions (1983)
    Springer
    Theoretical chemistry accounts 63 (1983), S. 401-419 
    Details
    ISSN: 1432-2234
    Keywords: Graphical representation of potential hypersurfaces ; MO and HL models ; Radical reactions ; Three-centre three-electron system ; VB calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A graphical representation of the potential energy hypersurfaces of the three-centre three-electron problem is proposed which is sufficient to fully describe the system. This method is used to visualize the hypersurfaces of the ground and the first excited doublet state of H3, obtained from VBCI calculations as well as from a judiciously parametrized HMO model and a semiempirical HL model. On the basis of these results three prototype radical reactions are discussed and the performance of the semiempirical models is assessed by comparison with theab initio results, in order to see which features of the models are essential for a correct description of radical reactions. The importance of overlap within the MO approach and of electron interaction within the semiempirical HL method is thus revealed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553614
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio and model hypersurfaces for ground and excited state radical reactions (1983)
    Springer
    Theoretical chemistry accounts 63 (1983), S. 401-419 
    Details
    ISSN: 1432-2234
    Keywords: Graphical representation of potential hypersurfaces ; MO and HL models ; Radical reactions ; Three-centre three-electron system ; VB calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A graphical representation of the potential energy hypersurfaces of the three-centre three-electron problem is proposed which is sufficient to fully describe the system. This method is used to visualize the hypersurfaces of the ground and the first excited doublet state of H3, obtained from VBCI calculations as well as from a judiciously parametrized HMO model and a semiempirical HL model. On the basis of these results three prototype radical reactions are discussed and the performance of the semiempirical models is assessed by comparison with theab initio results, in order to see which features of the models are essential for a correct description of radical reactions. The importance of overlap within the MO approach and of electron interaction within the semiempirical HL method is thus revealed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02399169
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  • 6
    Electronic Resource
    Electronic Resource
    Self-consistent group calculations on a simple model for the photochemical α cleavage reaction of carbonyl compounds (1987)
    Springer
    Theoretical chemistry accounts 72 (1987), S. 35-46 
    Details
    ISSN: 1432-2234
    Keywords: α Cleavage reaction of carbonyl compounds ; Excited state potential energy surfaces ; Photochemical reactions ; VB-CI
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Potential energy surfaces were calculated for the ground and some excited states of formaldehyde as a model for the α cleavage reaction of carbonyl compounds. Computations were based on an STO-3G basis within the SCGF approach. Only planar geometries were considered. The VB-CI description of the group of electrons directly involved in the reaction allows for a general and illuminating discussion of the wave functions for this reaction and gives a theoretical justification of the configuration mixing model of Pross [8].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526552
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  • 7
    Electronic Resource
    Electronic Resource
    A model for free-radical reactions (1985)
    Springer
    Theoretical chemistry accounts 67 (1985), S. 485-490 
    Details
    ISSN: 1432-2234
    Keywords: Potential energy hypersurfaces of H3 ; three-centre three-electron problem ; unpolar radical reactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Using an EHT type Hamiltonian the Heitler-London-VB treatment of the three-centre three-electron problem is simplified such that the interesting features of the potential hypersurfaces of arbitrary three-centre three-electron systems can be obtained simply from the knowledge of atomic orbital energies and overlap integrals. The method is applied to the hypersurfaces of the H3 system and extensions of the discussion of general radical reactions are indicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00528143
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  • 8
    Electronic Resource
    Electronic Resource
    Nichtnachbar-Matrixelemente in der HMO-Methode (1968)
    Springer
    Theoretical chemistry accounts 9 (1968), S. 339-343 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Zusammenfassung Die Grundlagen der vervollständigten HMO-Methode von Leupold [6] werden an Hand einiger Zahlenbeispiele untersucht.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00529929
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  • 9
    Electronic Resource
    Electronic Resource
    Pariser-Parr-Pople-Rechnungen an Molekülen mit Aminogruppen (1966)
    Springer
    Theoretical chemistry accounts 5 (1966), S. 251-265 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Abstract The results of PPP-calculations for cyanines, merocyanines, and aminoquinones agree well with the experimental electronic and vibrational spectra. The spectrum of 2,5-diaminobenzoquinone-1,4 must be considered as a p-benzoquinone-spectrum which under the influence of substituents has undergone a redshift. Also the charge distribution of this diaminoquinone is only slightly different from that of the quinone. These results tend to verify the assignment of the IR-spectra of the aminoquinones as given by Draber and Wallenfels and show that in the case of the aminoquinones the quinone character is so strong that it does not appear to be necessary to formulate them as a quadrupole-merocyanine.
    Abstract: Résumé Les résultats de calculs PPP pour des cyanines, des merocyanines et des aminoquinones sont en bon accord avec les spectres électroniques et vibrationnels expérimentaux. Le spectre de la 2,5 diamino benzoquinone-1,4 doit être interprété comme un spectre de p-benzoquinone déplacé vers les grandes longueurs d'onde sous l'influence du substituant. De même la répartition des charges de cette diamino quinone se distingue très peu de celle de la quinone. Ces résultats confirment le classement des spectres I.R. des aminoquinones dû à Draber et Wallenfels et montrent que le caractère quinonique des aminoquinones est si marqué qu'il paraît superflu de les considérer comme des merocyanines-quadrupolaires.
    Notes: Zusammenfassung Die Ergebnisse von PPP-Rechnungen für Cyanine, Merocyanine und Aminochinone stehen in guter Übereinstimmung mit den experimentellen Elektronen- und Schwingungsspektren. Das Spektrum des 2,5-Diaminobenzochinons-1,4 muß als unter Substituenteneinfluß langwellig verschobenes p-Benzochinonspektrum gedeutet werden. Auch die Ladungsverteilung dieses Diaminochinons unterscheidet sich nur sehr wenig von derjenigen des Chinons. Diese Ergebnisse stützen die Zuordnung der IR-Spektren der Aminochinone von Draber und Wallenfels und zeigen, daß in den Aminochinonen der Chinoncharakter so ausgeprägt ist, daß es unnötig erscheint, sie als Quadrupol-merocyanine zu formulieren.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00526938
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