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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 1760-1772 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical analysis and results of calculations are put forward to interpret the energies −εk of the occupied Kohn–Sham (KS) orbitals as approximate but rather accurate relaxed vertical ionization potentials (VIPs) Ik. Exact relations between εk and Ik are established with a set of linear equations for the εk, which are expressed through Ik and the matrix elements εkresp of a component of the KS exchange-correlation (xc) potential vxc, the response potential vresp. Although −Ik will be a leading contribution to εk, other Ij≠k do enter through coupling terms which are determined by the overlaps between the densities of the KS orbitals as well as by overlaps between the KS and Dyson orbital densities. The orbital energies obtained with "exact" KS potentials are compared with the experimental VIPs of the molecules N2, CO, HF, and H2O. Very good agreement between the accurate −εk of the outer valence KS orbitals and the corresponding VIPs is established. The average difference, approaching 0.1 eV, is about an order of magnitude smaller than for HF orbital energies. The lower valence KS levels are a few eV higher than the corresponding −Ik, and the core levels some 20 eV, in agreement with the theoretically deduced upshift of the KS levels compared to −Ik by the response potential matrix elements. Calculations of 64 molecules are performed with the approximate vxc obtained with the statistical averaging of (model) orbitals potentials (SAOP) and the calculated εk are compared with 406 experimental VIPs. Reasonable agreement between the SAOP −εk and the outer valence VIPs is found with an average deviation of about 0.4 eV. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 75 (1971), S. 1549-1551 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 88 (1984), S. 1479-1481 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 11 (1968), S. 205-209 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Mittels früherer Ergebnisse für Bindungskräfte bei zweiatomigen Molekülen werden Neben-bedingungen für die Wellenfunktion formuliert. Es ist anzunehmen, da\ dies zu einer Verbesserung der Berechnung für die entsprechenden Kraftkonstanten führt.
    Abstract: Résumé Les résultats d'études antérieures des forces et des constantes de force diatomiques sont utilisés pour formuler des contraintes de force. De telles variations contraintes devraient améliorer les calculs de constante de force.
    Notes: Abstract The results of earlier studies of diatomic forces and force constants are used to formulate force constraints. It is proposed that such constrained variations should improve force constant calculations.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 13 (1969), S. 159-161 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Further investigation is made on the use of off-diagonal hypervirial theorems as constraints. Firstly, it is found that an energy-independent off-diagonal constraint is not useful in improving calculation of transition probabilities. Secondly, when the approximate wavefunction is flexible enough, iteration on the transition energy converges very rapidly. Finally the study is extended to the isoelectronic species Li+ and Be+2.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 50 (1978), S. 181-184 
    ISSN: 1432-2234
    Keywords: Ketene, vertical ionization potentials of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The vertical ionization potentials of ketene are calculated by perturbation corrections to Koopmans' theorem. The present results are compared with those from the pseudonatural orbital coupled electron pair approach and the experimental values.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 17 (1970), S. 259-263 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Die erweiterte Geminaltheorie wird auf den Grundzustand des BH für R=2,329 Bohr angewendet. Es wird gefunden, daβ der Einschluβ von nur „Ein-Elektron-Transfer“-Konfigurationen zu einer Energieerniedrigung von ∼0,01 Hartree, verglichen mit der antisymmetrisierten Geminal-Produkt-Wellenfunktion, führt. Diese Verbesserung beträgt mehr als 90% gegenüber dem Wert, der mit einer vollen CI-Funktion erreicht wird. Ein „kontrahierter“ doppelt-zeta-Basis-Satz liefert ebenfalls gute Ergebnisse.
    Abstract: Résumé La théorie des géminales généralisée est appliquée à l'état fondamental de BH pour R=2,329 bohr. On trouve que l'introduction des seules configurations à «un transfert d'électron» conduit à un abaissement de l'énergie de ∼0,01 hartree, par rapport à celle correspondant à un simple produit antisymmétrisé de géminales. Cette amélioration est supérieure à 90% de celle obtenue par I.C. complète. Une base double zèta «contractée» s'avère aussi fort bonne.
    Notes: Abstract Extended geminal theory is applied to the ground state of BH at R=2.329 bohr. It is found that the inclusion of only “one-electron transfer” configurations leads to a lowering in the energy of ∼0.01 hartree, compared to the antisymmetrized geminal product wavefunction. This improvement is 〉90% of that achieved by a full configuration-interaction wavefunction. A “contracted” doublezeta basis set is also found to be quite good.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 10 (1968), S. 364-366 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is shown that Löwdin-orthogonalised Slater-type orbitals yield reasonable spin densities in the case of the trimethylene-methyl- and allyl radical.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 12 (1968), S. 175-177 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simple procedure is outlined, to obtain good initial guesses for the parameters for multiple constraints.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 12 (1968), S. 337-340 
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A new method is proposed for solving constrained secular equations. It incorporates the two methods which have been used so far, namely, perturbation and parametrization. The present method has the advantages of both of the previous methods and none of their disadvantages. This is illustrated by an example.
    Type of Medium: Electronic Resource
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