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  • 1
    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 screened-Coulomb exchange model used first in the Xα method and later on in Kohn-Sham density functional theory is reexamined. Based on the well-elaborated framework of the local spin-density approximation, we show that this model is not well suited when systems with a finite number of electrons are concerned, because it does not respect the pair-density sum rule. A proper modification of the model is proposed by reformulating it in terms of a screened-exchange hole and ensuring the sum rule for this hole. As a result, it is shown how the static screened exchange in finite systems is accompanied by a conjugate antiscreened one. The possible consequences of this effect on the application of the screened-Coulomb exchange model are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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 current capabilities of density functional theory reach their limits somewhere in the region of weak inter- and intramolecular interactions. Hydrogen bonds can be treated, but not perfectly. The few results that have been obtained for dispersion-dominated van der Waals interactions are erratic. The generalized gradient approximation fails for charge-transfer complexes; hybrid functionals that incorporate a component of the Hartree-Fock exchange are promising, but the results depend strongly on the variant used. We recently used the adiabatic connection and coordinate scaling to develop correlation functionals based on a spin-polarized pair correlation function of the Colle-Salvetti type. A résumé of the current status of the functionals is given, including inter alia available validation results for various molecules and reactions, the water dimer, and charge-transfer complexes. It is shown that nonlocal schemes involving the kinetic energy density and, hence, the Laplacian of the electron density lead to an overall improvement of the calculated binding energies and equilibrium geometries, especially in cases when the current GGA schemes meet difficulties. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetic energy density-dependent correlation functional LAP1 is extended to include parallel-spin correlation beyond the exchange level. Two exchange-correlation schemes are considered, combining the new correlation functional (LAP3) with the GGA exchange of Becke and the GGA exchange of Perdew. Extensive tests on molecules and hydrogen-bonded systems are presented and discussed elucidating the role of parallel-spin correlation in different cases. Its inclusion in the LAP functional leads, on average, to a slight improvement of the calculated binding energies and equilibrium geometries of molecules. Particularly high sensitivity of the energy results on the relative share of parallel-spin correlation is observed for aromatic molecules and for systems involving weak hydrogen bonds.   © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 427-446, 1997
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
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