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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2343-2353 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The partitioning of electron correlation energy into dynamical and nondynamical components is examined in the context of the local-scaling transformation version of density-functional theory. An assessment is made of the relative importance of these components for the beryllium atom and its isoelectronic sequence. In particular, the problem of finding a multiconfiguration reference wave function differing only in dynamical correlation from the exact wave function is considered. It is shown that to a good approximation this reference wave function is given by Ψ=C11s22s2+C21s22p2. The concepts of "long-range" and "short-range" correlation are re-examined from a perspective based on the reference wave function. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 6722-6731 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report energy calculations of selected first-row atoms using explicit approximate Hartree-Fock functionals generated in the context of the local-scaling version of density functional theory. We show that these approximate functionals yield highly accurate upper bounds to the Hartree-Fock energies of the atoms considered. The generation of molecular functionals in terms of local-scaling transformations centered at each nucleus is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9227-9235 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The partitioning of electron correlation energy into dynamical and nondynamical components is examined in the context of the local-scaling transformation version of density-functional theory and its connection with the Hohenberg–Kohn–Sham density-functional-theory definition of electron correlation is discussed. The relative importance of these components is analyzed with reference to the helium atom and its isoelectronic series. The present results attest to the preponderantly dynamical character of the recovered correlation energy. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    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: It is shown that any expectation value of any observable associated with a molecule is the sum of loge contributions and of loge pair contributions. This result provides a rigorous theoretical basis for the study of additive properties of molecules.It is demonstrated that molecular wave functions (exact or approximate) can be expressed as a sum of functions corresponding to the various electronic events. Furthermore any of these event functions can be expressed in terms of correlated loge functions. This expression suggests many kinds of variational procedures of calculating wave functions (known methods and new ones).The case in which noncorrelated completely localized loge functions are used is discussed. If continuous functions are used the variational equation reduces to a sum of independent variational equations, each one corresponding to a particular electronic event. This is not so when discontinuous functions are used or when a delocalized function is added to replace the correlation interloge function.The noncorrelated completely localized loge model is analyzed in more detail. It is seen that local spin operators can be introduced and that each event density operator is the product of the loge density operators. Therefore that model is an independent loge model. The corresponding generalized self-consistent field equations are derived. This treatment helps us to understand how a localized state of a molecule can produce an ion containing a delocalized region, a phenomenon which is sometimes at the origin of some misunderstanding in photoelectron spectroscopy. Finally it is seen how virtual loge functions can be introduced to describe excited states.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 5 (1971), S. 395-409 
    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 model of complete loge localization is employed here to develop a practical method for handling correlation effects in atomic and molecular many electron systems. Intraloge correlation is dealt with by an independent variational treatment of pair functions which are continuous and vanish outside a given loge. It is shown that in the context of the model it is possible to compute pair correlation energies for localized single and double bonds in molecules by evaluating only modified atomic integrals. We bypass in this manner the evaluation of multicenter integrals necessary in other formalisms. In addition, the corrections to the model are discussed and in particular it is shown that part of the interloge correlation effects are already described by the loge localized wave function.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 70 (1998), S. 591-600 
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new model for the exchange potential in the framework of DFT is proposed. The potential is defined as 2αx∊xappr, where ∊xappr is the exchange-energy density and αx is not a constant but a functional αx[ρ] to be determined iteratively. The exact Fock expression and the LDA, GEA, and Becke88 approximations were used as ∊xappr. We provide results for atoms showing that this model potential yields total and exchange energies and other atomic properties that are in good agreement with Hartree-Fock values. In addition, total energies obtained by adding to the αx[ρ] approach correlation energy corrections computed via the WL and LYP functionals are in close accord with experimental values.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 591-600, 1998
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 485-496 
    ISSN: 0020-7608
    Keywords: Hartree-Fock ; local-scaling DFT ; DFT ; lithium ; beryllium ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We advance a reformulation of the Hartree-Fock problem in the context of the local-scaling transformation version of density functional theory. Explicit functionals of the energy are obtained. These functionals are expressed in terms of both the one-particle density and the local-scaling transformation function - itself an implicit function of the one-particle density. Variational calculations for the lithium and beryllium atoms based on these functionals yield upper bounds to the Hartree-Fock energies that are undistinguishable from the Clementi-Roetti values. Moreover, evaluation of these optimized functionals at the one-particle densities obtained from the 12-term Raffenetti orbitals yield the limiting values for the Hartree-Fock energies for these atoms.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 485-496, 1998
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 503-512 
    ISSN: 0020-7608
    Keywords: density functional theory ; local-scaling transformations ; kinetic-energy functionals ; exchange-energy functionals ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using several types of simple generating orbitals, explicit expressions for the kinetic-energy functional Ts[ρ] and the exchange functional Ex[ρ] were generated in the context of the local-scaling transformation version of density functional theory. The variational parameters in these orbitals were optimized by a minimization of either the kinetic-energy functional (Kohn-Sham procedure) or the total-energy functional (Hartree-Fock procedure) corresponding to a single Slater determinant. The results obtained for several atoms show that the present kinetic-energy functionals yield values whose percent error is at least an order of magnitude smaller than that of the best available functionals.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 503-512, 1998
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 69 (1998), S. 439-450 
    ISSN: 0020-7608
    Keywords: local scaling transformation ; electron correlation ; DFT ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We discuss in the present work the treatment of electron correlation within the context of the local scaling transformation version of density functional theory. This is done by resorting to a locally scaled transcorrelated Hamiltonian of Boys and Handy [S. F. Boys and N. C. Handy, Proc. Roy. Soc. A310, 43 (1969)] which describes electron correlation effects as arising from the action of effective two- and three-particle terms on a single Slater determinant. The expectation value of the locally scaled correlated wave function is expressed in terms of the factor Aviles-Hartog-Tolhoek (FAHT) cluster expansion, and the explicit form of the correlation functional is given up to second order. In particular, an explicit analytic functional is obtained for the effective two-body term. This functional contains ρ5/3, ρ4/3, and ρ2/3 as universal factors. Numerical calculations using the locally scaled correlation wave function are performed for two-electron atoms for which various types of orbitals and correlation factors are tested. The numerical results for the correlation energy of these two-electron systems attest as to the adequacy of the present locally scaled-generated functionals.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 439-450, 1998
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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