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  • 1
    Electronic Resource
    Electronic Resource
    A local density-functional study of the electron density distribution in the H2O dimer (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5787-5793 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Accurate local density-functional calculations of the electron density distribution in the H2O dimer are performed and, in order to distinguish intramolecular charge shifts from intermolecular charge transfer, analyzed in terms of an expansion in atom-centered multipole moments. The dependence on basis set and basis set superposition error of the electron density redistribution upon forming the hydrogen bonded complex has been examined. A model study reveals that only strong hydrogen bonds induce electron density redistributions large enough to be observable by means of x-ray diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455554
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  • 2
    Electronic Resource
    Electronic Resource
    Electrostatic interactions in host–guest complexes. I (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 1121-1125 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In the first article of this series a study of the K+ ⋅⋅⋅H2 O interaction is presented. The calculations are done with the local density approximation using the Xα-LCAO-DVM approach. The polarization of the water molecule in the complex are compared with the polarization of water in several electrostatic fields (homogeneous field, point charge, field of K+ cation). The effect of exchange repulsion on the polarization is analyzed. A decomposition of the interaction energy as computed in the Xα approach is carried out. This shows that the various effects of the interaction are well reproduced by this approach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457184
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  • 3
    Electronic Resource
    Electronic Resource
    Electron density distributions in hydrogen bonds: A local density-functional study of α-oxalic acid dihydrate and comparison with experiment (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4199-4208 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Accurate local density-functional calculations of the electron density distribution in α-oxalic acid dihydrate, C2H2O4⋅2H2O, are performed and compared with experimental densities obtained from high-resolution x-ray diffraction measurements at 100 K. Results are corrected for basis set superposition errors. The agreement between the vibrationally averaged theoretical and experimental density improves significantly when taking into account the effects of hydrogen bonding and crystal environment. Electron density redistributions due to strong hydrogen bonds are found to outweigh the experimental standard deviation only in the bond region of the molecules involved as donor of the hydrogen bond.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454855
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  • 4
    Electronic Resource
    Electronic Resource
    A test on the statistics of derived intensities (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 1011-1013 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Variances of X-ray reflexions calculated with the procedure as proposed by McCandlish, Stout & Andrews [Acta Cryst. (1975), A31, 245-249] have been tested against variances determined in an independent way. A satisfying agreement is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773947600209X
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular form factors in X-ray crystallography (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 444-450 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The calculation of molecular form factors from ab initio molecular electronic wavefunctions is discussed, and a scheme for application to X-ray diffraction structure analysis is given. The method is used to calculate the form factor of the NH+4 molecular ion from three accurate molecular wavefunctions, as well as for the corresponding isolated-atoms arrangement. The merits of the different form factors obtained are tested on experimental single-crystal X-ray diffraction data for NH4F. It appears that the quality of the form factor is determined by the number of centres in the wavefunction basis rather than by the wavefunction energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739469000891
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  • 6
    Electronic Resource
    Electronic Resource
    X-ray scattering and the chemical bond in N2 and CN− (1971)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 27 (1971), S. 487-491 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray scattering from the chemical bond within N2 and CN− has been studied in detail. Differences in scattering from these systems, derived from bonding and non-bonding models, are characterized by R values of ̃0.04. Partitioning of the scattering into core and valence electron parts clearly demonstrates that the bonding effects are completely situated in the valence electron structure of the systems. Therefore, new evidence has been contributed to support valence structure analysis methods presently employed in X-ray diffraction structure studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739471001049
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  • 7
    Electronic Resource
    Electronic Resource
    Electron and magnetization densities in molecules and crystals edited by P. Becker (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1092-1093 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480002239
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  • 8
    Electronic Resource
    Electronic Resource
    Electrostatic molecular interaction from X-ray diffraction data. II. Test on theoretical pyrazine data (1983)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 14-21 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In a previous paper [Moss & Feil (1981). Acta Cryst. A37, 414-421] a method was reported to calculate the electrostatic potential and the electrostatic interaction energy from single-crystal X-ray diffraction data. The method was applied to experimental pyrazine data; however, owing to the relatively low quality of the data, the results were inconclusive. In the present paper the results are presented of a model study in which the method has been applied to the analysis of ideal error-free diffraction data calculated from a theoretical wavefunction. The molecular quadrupole moments and the electrostatic interaction energies of two pyrazine molecules thus obtained are in very good agreement with the corresponding results derived directly from the wavefunction. Thus the proposed method may be used to determine the long-range electrostatic component of molecular interactions from highly accurate X-ray diffraction data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767383000021
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  • 9
    Electronic Resource
    Electronic Resource
    A theoretical study of elastic X-ray scattering (1980)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 503-509 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Bragg X-ray scattering intensities are defined as scattering by the thermodynamic average electron-charge density. Purely elastic, kinematic X-ray scattering by a target in thermal equilibrium is always larger than Bragg scattering. At low temperatures, the elastic scattering becomes Bragg scattering. For large molecules, such as a crystal, at ordinary temperatures the elastic and Bragg scattering differ in a relative sense by O(N-1), where N is the number of vibrational degrees of freedom. For most practical cases the Bragg scattering is essentially the same as purely elastic scattering of X-rays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739480001155
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  • 10
    Electronic Resource
    Electronic Resource
    The structure of NH4F as determined by neutron and X-ray diffraction (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 438-444 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Neutron and X-ray intensities of NH4F were measured at −196°C and −155°C respectively. The wurtzite type structure and space group P63mc were confirmed. The displacement of the two h.c.p. sublattices, formed by each of the F−- and NH+4- ions, is such that all bond-distances are equivalent. The N–H bond distances as found from the X-ray data are about 0.1 Å shorter than those obtained from the neutron data. The final weighted R values were 1.9% and 2.6% for the X-ray and neutron data respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773946900088X
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