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  • 1
    ISSN: 1432-2234
    Keywords: Electron correlation ; H2 ; LiH ; BH ; Statistical correlation coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Electron correlation in the H2, LiH and BH molecules has been analyzed in terms of the statistical correlation coefficients introduced by Kutzelnigg, Del Re, and Berthier. Angular, radial (in-out), longitudinal (left-right) and transverse correlation coefficients have been evaluated from both self-consistent-field (SCF) and configuration interaction (CI) wave functions. It has been found that these coefficients reflect fairly well the correlation behavior in the molecular system. The lack of spherical symmetry in molecular densities adds new features to these correlation coefficients and this information can be useful for the study of electronic structure in molecules. The correlation hole function, Fermi and Coulomb holes in these systems have also been calculated and discussed.
    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 104 (1996), S. 4850-4858 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this article, a mathematical description of spin diffusion in copolymers is presented that avoids some of the approximations employed by previous authors. The analytical relations obtained can readily be used in solid-state NMR experiments to determine the domain size of each component. A numerical approach to spin diffusion has also been examined and its performance has been compared with the analytical method. For systems with interphase structure, the spin diffusion process has been numerically simulated based on a simple model with linear character changes. Application of the present method to systems with or without interphase has been demonstrated. © 1996 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 3477-3480 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple formalism for the evaluation of 〈S2〉 in terms of the two-particle density matrix is presented. The implementation of the formalism in the restricted open-shell Hartree–Fock (ROHF), unrestricted HF (UHF) and density functional (DFT) based theories is discussed. Rules governing the nonzero S2 matrix elements in the UHF based methods are presented. Further examples are given of 〈S2〉 in several atomic and radical systems from very simple density functional models. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4842-4854 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The total, inelastic and elastic intensities for x-ray and high energy electron scattering from the ten-electron molecules CH4, NH3, H2O, and HF have been calculated with configuration interaction wave functions. The probability density of the interelectronic distance or the radial intracule density is extracted from the intensities. The importance of basis sets, chemical binding, and electron correlation to the scattered intensities and the radial intracule density has been examined. It has been found that scattered intensities predicted with correlated wave functions agree well with experiment. Based on the electron pair distribution, the exchange and correlation holes in molecular systems have been briefly discussed.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 9188-9194 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electron intracule and extracule densities of the neon atom, the hydrogen molecule, and lithium hydride have been studied using both correlated and self-consistent-field (SCF) wave functions. For the first time, the effects of electron correlation on the anisotropic intracule and extracule densities are simultaneously displayed and analyzed.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1016-1020 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model which treats spin diffusion and spin-lattice relaxation in multiphase polymers on the same footing is proposed. This new approach allows for more accurate determination of domain sizes and interfacial thickness in the probed polymers. In a poly(styrene-b-isoprene) copolymer example a significant improvement in the agreement between the NMR measurements and the simulated results can be obtained with the incorporation of a spin-lattice relaxation term into the spin diffusion process. The obtained microphase structural parameters are similar to the small angle X-ray scattering results. In addition, the spin-lattice relaxation times (T1) in different domains can be predicted reasonably well based on T1s of the component homopolymers and on the microphase structure in the present model. © 1997 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 6693-6698 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new semiquantitative measure of the difference between two electron density distributions is proposed. Specifically, the natural orbitals of an accurate electron density, such as those given by a configuration interaction method, are used to expand the Kohn–Sham orbitals of an approximate density functional method. The difference between the two density distributions is then reduced to a single number, the orbital-based density difference index (DDI). With the reference densities calculated from quadratic configuration interaction calculations including single and double substitutions, DDIs were obtained for four diatomic molecules using three basis sets and seven approximate functionals. Results are also included for an additional six small molecules with a flexible extended basis set and the same set of functionals. These results show that the DDI leads to conclusions that are consistent with those obtained previously by visual comparison of density difference plots. The orbital-based density difference indices are very dependent on the choice of the functional, but are fairly stable with respect to the choice of the basis set. © 1997 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 9745-9755 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The one-electron density, and intracule (relative motion p=p1−p2) and extracule [center of electron mass P=1/2(p1+p2)] pair densities for the first-row hydrides (LiH–FH) in their ground states have been calculated from both self-consistent-field (SCF) and configuration interaction (CI) wave functions. For each molecule, the anisotropic, radial, and projected one-electron and pair densities along (longitudinal) and perpendicular (transverse) to the molecular axis are displayed and analyzed. The moments of the one-electron and pair distributions in momentum space are also discussed. The effect of electron correlation on these momentum densities and moments have been studied.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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 electron-pair (intracule and extracule) densities of the first-row hydrides may be understood on the basis of the different chemical-bonding schemes in this series. Thus, the LiH pair densities show a strongly ionic nature and may be fairly well described by Li+H-. The CH-pair densities, on the other hand, may be approximated by the promolecular superposition of a carbon and a hydrogen atom with an accumulation of pair density in the internuclear region signifying covalency. In the case of FH, its pair densities show a predominately ionic structure and are closer to those of F- than to those of the promolecular superposition of a fluorine and a hydrogen atom. The slight deformation of longitudinal pair densities observed in FH is largely due to the presence of the H+. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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: Correlation holes of electrons with the same (Fermi hole) and different (Coulomb hole) spins in the ground (X1Σ+), first (A1Σ+) and second (B1II) excited states of LiH were constructed from full configuration interaction (CI) wave functions. It was found that the shapes of both the Fermi and Coulomb holes in these states are dependent on the location of the reference electron. When the reference electron is chosen to be close to the Li nucleus, the Fermi correlation results in a large negative hole for all three states. However, the A1Σ+ excited state is further characterized by displaying a second hole around the H nucleus, and in the B1II state, the hole is elongated along the molecular axis. Coulomb correlation shows up strongly in the A1Σ+ state and, in addition, there is clearly correlation of electrons at the two nuclei. These features of the correlation holes were compared with those from a two-Slater-determinant model wave function. The Hartree, Fermi, and Coulomb screening potentials in these states were also studied in the light of possible modeling of the correlation functionals for the excited states. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
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