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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 333-347 
    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 nonlocal weighted density approximation (WDA) to the exchange and kinetic energy functionals of many-electron systems proposed several years ago by Alonso and Girifalco in the context of density functional theory is used to compute, within the framework of the spherical jellium model, the ground-state electronic density, chemical potential, and total energy of neutral and negatively and positively charged sodium clusters containing up to N = 800 atoms. From these calculations, we study the behavior of the total energies per atom, chemical potentials, ionization potentials, I(N), and electron affinities, A(N). These results are compared with analogous calculations using the well-known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximation for the kinetic (TFW) and exchange (D) energy functionals. Calculations including the local density approximation (LDA) to the correlation energy in both WDA and TFWD functionals are also presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 499-508 
    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 local density approximation (LDA) to exchange and correlation effects has well-known limitations. The nonlocal weighted density approximation (WDA) corrects some of those defects. This is illustrated here by applications to free atoms and small atomic clusters. The WDA also induces a nonlocal kinetic energy functional that is tested for atoms. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 347-358 
    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 nonlocal weighted density approximation (WDA) to the exchange and kinetic-energy functionals of many electron systems proposed several years ago by Alonso and Girifalco is used to compute, within the framework of density functional theory, the ground-state electronic density and total energy of noble gas atoms and of neutral jellium-like sodium clusters containing up to 500 atoms. These results are compared with analogous calculations using the well known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximations for the kinetic (TFW) and exchange (D) energy density functionals. An outstanding improvement of the total and exchange energies, of the density at the nucleus and of the 〈r-1〉 expectation values is obtained for atoms within the WDA scheme. For sodium clusters we notice a sizeable contribution of the nonlocal effects to the total energy and to the density profiles. In the limit of very large clusters these effects should affect the surface energy of the bulk metal. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 567-573 
    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 study of the coronene - coronene association using different interaction potentials based on an atom-atom pair potential proposed by Fraga has been performed. The interaction potentials employed differ in the way the electrostatic and/or dispersion contributions are computed. The influence of both contributions on the geometries predicted for the coronene dimer is discussed in order to analyze the effectiveness of the different interaction potentials. The stationary points found in each interaction energy hypersurface are characterized by calculating the Hessian eigenvalues. Results are discussed in the light of those previously reported for the benzene dimer. Stacked-displaced structures are suggested to be the preferred conformations for the coronene - coronene association. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 993-1010 
    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: We calculate the first ionization potential of atoms (3 ≤ Z ≤ 54) by means of a nonlocal density functional approach and the results are compared with those obtained using other recent density functional approaches based on density gradients. In these calculations, we use a nonlocal weighted spin-density approximation of exchange effects and a local spin-density approximation of Coulomb correlation, both based on novel forms of the pair-correlation functions. We also calculate the total energies of the He, Be, and Ne isoelectronic series. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 49 (1994), S. 171-184 
    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 search for a density functional theory (DFT) free of one-electron orbitals needs the development of good kinetic energy functionals beyond the venerable Thomas-Fermi and gradient expansion functionals. With this goal in mind, we previously solved for several atoms and positive ions the Euler equation associated with the exchange and kinetic energy functionals of the nonlocal weighted density approximation (WDA). In this work, we improve the theory by enforcing the correct asymptotic behavior of the exchange potential following a prescription of Przybilsky and Borstel (PB). We have calculated electronic densities, density moments 〈rn〉 (n = -1,1,2) and the density at the nucleus ρ(0), as well as total and exchange energies and chemical potentials for neutral and charged atoms. All those quantities show a better agreement with Hartree-Fock results than those obtained using gradient-corrected Thomas-Fermi functionals. The radial densities, 4πr2(r), show two local maxima at positions close to those of the first two maxima of Hartree-Fock radial densities. This effect, which is absent in the self-consistent densities from the usual gradient-corrected Thomas-Fermi functions, can be interpreted, in our view as an incipient emergence of the shell effect. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 13 (1992), S. 148-154 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The performance of Atomic Natural Orbital (ANO) basis sets for calculations involving nonempirical core pseudopotentials has been studied by comparing the results for atomic and molecular nitrogen obtained using contracted ANO basis sets with those obtained using both the primitive set and a segmented one. The primitive set has been optimized at the SCF level for atomic N treated as a five-electron pseudo-atom, and consists of 7s and 7p primitive GTOs supplemented by 2d and 1f GTOs optimized at the CI level. From this primitive set three contracted [3s 3p 2d 1f] sets have been obtained. The first one has been derived from the ANOs of the neutral atom, the second has been obtained from an averaged density matrix and the third one is a segmented set. For the atom, the segmented set gives a zero contraction error at the SCF level as it must be in valence-only calculations. The ANO basis sets show some small contraction error at the SCF level but perform better in CI calculations. However, for the diatomic N2 molecule the ANO basis sets exhibit a rather large contraction error in the calculated SCF energy. A detailed analysis of the origin of this error is reported, which shows that the conventional strategy used to derive ANO basis sets does not work very well when pseudopotentials are involved.
    Additional Material: 6 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 647-654 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The importance of characterizing the stationary points of the intermolecular potential by means of Hessian eigenvalues is illustrated for the calculation of the benzene-benzene interaction using an atom-to-atom pair potential proposed by Fraga (FAAP). Two models, the standard one-center-per atom and another using three-centers-per atom due to Hunter and Sanders, are used to evaluate the electrostatic contributions and the results are compared. It is found in both cases that although using low-gradient thresholds allows optimization procedures to avoid many stationary points that are not true minima computing time considerations makes the usual procedure of using high-gradient thresholds [say, 10-2 kj/(mol Å)] as the most efficient. Moreover, this later procedure can be recommended because the actual minima can be characterized by means of Hessian eigenvalues even if these high-gradient thresholds are used, and further decreasing of the convergence criterion does not imply significant modifications in the geometric parameters of the minima. The possible advantages of using the three-centers-per-atom model for the calculation of molecular associations between delocalized systems are also discussed on the basis of the agreement of the benzene-benzene results with experimental and theoretical data taken from the literature. © 1993 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 14 (1993), S. 680-684 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A simple procedure devised to obtain optimized point charges to represent the Madelung potential is reported and applied to six different crystal structures occurring in ionic systems. Their use in ab initio cluster model calculations is discussed through some selected examples and results compared with those arising from the use of the well-known Evjen method. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 9 (1988), S. 836-843 
    ISSN: 0192-8651
    Keywords: Computational Chemistry and Molecular Modeling ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: The possible Cs, C2v, and C∞v structures of AlO2 corresponding to the two lowest electronic states which dissociate into the neutral Al(2P) and O2(3Σg-) fragments have been investigated at the ab initio self-consistent field (SCF) and CI levels using nonempirical pseudopotentials. The most stable structure corresponds to a C2v symmetry in the 2A2 electronic state. However, this structure presents the three-center three-electron Hartree-Fock instability and CASSCF calculations were necessary to unequivocally characterize it as true minimum. Moreover, only another stable structure, of C2v geometry, was found to be a minimum, corresponding to a low-lying excited state of 2A1 symmetry. The optimized C∞v structures were not minima on the corresponding potential energy surfaces and no evidence of any stable Cs structure was found. Calculating values are compared with the different experimental data obtained from the reaction of Al and O2 in frozen gas inert matrices.
    Additional Material: 2 Tab.
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