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  • 11
    Electronic Resource
    Electronic Resource
    The question of the completeness of the natural orbitals with nonzero occupation numbers for atoms and molecules (1993)
    Springer
    Theoretical chemistry accounts 86 (1993), S. 3-11 
    Details
    ISSN: 1432-2234
    Keywords: Reduced density matrices ; Natural orbitals ; Extended Koopmans' theorem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The completeness of the natural orbitals with nonzero occupation numbers is examined for several model Hamiltonians and for the helium atom. It is demonstrated that whether the occupied natural orbitals form complete sets depends on the nature of the electron-electron interaction in the model Hamiltonian. Discrepancies in the extant proofs of the exactness and inexactness of the extended Koopmans' theorem are resolved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113512
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  • 12
    Electronic Resource
    Electronic Resource
    Introduction of Klaus Ruedenberg (1992)
    Springer
    Theoretical chemistry accounts 83 (1992), S. 5-13 
    Details
    ISSN: 1432-2234
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113239
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  • 13
    Electronic Resource
    Electronic Resource
    On the genesis of a theory (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 37 (1990), S. 327-347 
    Details
    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
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560370407
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  • 14
    Electronic Resource
    Electronic Resource
    Approximate density matrices and wigner distribution functions from density, kinetic energy density, and idempotency constraints (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 819-830 
    Details
    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: The Wigner distribution function and the corresponding density matrix are calculated using a form for the distribution function suggested by maximization of the entropy. Wigner functions and density matrices are determined by imposing conditions of idempotency on the density matrix. Exchange energies and Compton profiles calculated from density matrices obtained by imposing the idempotency constraints are compared with the results of calculations using the Hartree-Fock density matrix and a Gaussian approximation for the density matrix for H and the noble gases He through Xe. Compton profiles from Wigner functions with idempotency constraints show improvements over the Gaussian approximation for the lighter atoms, but do not show significant changes for the heavier atoms. Exchange energies from density matrices with idempotency constraints show improvements over the Gaussian approximation except for the heavier atoms Kr and Xe.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560380605
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  • 15
    Electronic Resource
    Electronic Resource
    On the redistribution of electrons for chemical reaction systemsAided by research grants from the National Science Foundation and the National Institutes of Health to the University of North Carolina (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 41 (1992), S. 527-555 
    Details
    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: A regional density-functional theory is formulated and applied to the study of ground-state electron redistributions during the course of a chemical reaction. If for a given increment of the reaction process, accumulation of electrons occurs in a certain region of space, then it is called the dynamic acceptor region, denoted by P. The complement is called the dynamic donor region, denoted by Q. The regional energy itself is determined as a unique functional of the electron density of the total system. The regional transfer potentials are defined in such a way that they add to give the total chemical potential, and their values along the reaction coordinate are found to be different between P and Q. The difference between the regional transfer potentials is shown to provide the driving force for electron transfer from Q to P. A characteristic coordinate for following electron transfer and an associated excitation potential are introduced. The excitation potential is a measure of regional virtual excitation due to regional interactions. The regional transfer potential gives the local character of electron transferability, while the excitation potential gives the global character. The theory encompasses the concepts of regional hardness and softness and sheds light on the HSAB principle.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560410402
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  • 16
    Electronic Resource
    Electronic Resource
    Approximate density matrices and Husimi functions using the maximum entropy formulation with constraints (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 823-837 
    Details
    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: The entropy of an electronic system is defined in terms of the Husimi function, a nonnegative distribution function in phase space. The Husimi function is calculated by maximizing the entropy subject to the constraints that the Husimi function give a Gaussian convolution of the desity when integrating over the momentum coordinates and that its second moment with respect to momentum give a sum of Gaussian convolutions of the density and the kinetic energy density. The result is compared with the Wigner function. Equations are given for calculating the density matrix from the Husimi function. The resulting equation for the exchange energy requires a difficult numerical integration. An alternate method is used to obtain the density matrix from an approximate partially collapsed Husimi matrix that gives the maximum entropy Husimi function as its diagonal. The results are exact for the harmonic oscillator ground state. Exchange energies calculated for H and the He isoelectronic series through C+4 show slight improvements over those calculated using a maximum entropy Wigner function.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560390607
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  • 17
    Electronic Resource
    Electronic Resource
    Companions in the search (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 739-770 
    Details
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560490515
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  • 18
    Electronic Resource
    Electronic Resource
    Thomas-Fermi-Dirac models of atoms constrained by nuclear cusp and long-range conditions (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 42 (1992), S. 1759-1769 
    Details
    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: The traditional Thomas-Fermi-Dirac model of the electronic structure for a neutral atom is deficient in that it predicts an infinite electron density at the nucleus and a sharp cutoff of the electron density at a finite radius. This study was carried out to remedy these faults in the model. Extending an idea used earlier in Thomas-Fermi (TF) theory [Proc. Natl. Acad. Sci. U.S.A. 83, 3577 (1985)], the Thomas-Fermi-Dirac (TFD) energy functional is minimized under constraints ∫ρ(r) dr = N, ∫e-2kr▽2ρ(r)dr 〈 ∞ and ∫(1 - e-k′r)ρ4/3(r)dr 〈 ∞, with k and k′ determined by the nuclear cusp condition and the correct asymptotic behavior. Optimum coordinate scaling also is considered. It is found that the TFD model is substantially improved by constraining the minimization search domain of the energy functional in this way. Energies are given for five noble gas atoms, and Compton profiles for these atoms are calculated. The behavior of electrons in momentum space is improved in both this modified TFD model and in the corresponding modified TF model.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560420613
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  • 19
    Electronic Resource
    Electronic Resource
    Publication list (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 135-144 
    Details
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560490305
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