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  • 1
    Electronic Resource
    Electronic Resource
    Dynamical scattering and electron crystallography - ab initio structure analysis of copper perbromophthalocyanine (1992)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 48 (1992), S. 562-568 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Electron diffraction intensity data were collected at 1200 kV from thin epitaxically oriented crystals of copper perbromophthalocyanine (C32Br16CuN8) in a projection down molecular columns. Measured cell constants for the projection with cmm symmetry are d100 = 17.88 (9), b = 26.46 (15) Å. The structure was determined by Fourier refinement after three heavy-atom positions were identified in an initial potential map. In addition to the copper and halogens, all light-atom positions were found. Although the final R value for all data is 0.41, n-beam dynamical calculations for crystal thicknesses corresponding to the estimated sample dimension account for the observed amplitudes that deviate most from their kinematical values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S010876739200206X
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  • 2
    Electronic Resource
    Electronic Resource
    Solution of the phase problem in crystallography and application to dynamical electron diffraction (1995)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 51 (1995), S. 708-716 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Unitarity, a fundamental principle of scattering theory, leads to the prediction of an essentially unique set of phases for the scattering amplitude from a complete knowledge of the differential cross section or, in the case of a crystal, from the diffracted intensities. The Sayre equation and all the direct methods of phasing following therefrom are derived as a special case of unitarity for zero excitation error. Dynamical and kinematical scattering are considered, and the relationship between them, \hat S = exp(iτnz\hat K), is obtained. Applications to the case of electron diffraction including for non-zero excitation error are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767395003278
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Electron diffraction from phospholipids – an approximate correction for dynamical scattering and tests for a correct phase determination (1993)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 26 (1993), S. 778-786 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An approximate experimental correction of electron diffraction intensities from an epitaxically crystallized phospholipid bilayer for dynamical scattering is described. This correction, which is useful for certain low-angle centrosymmetric data sets, compares intensities recorded at high and low electron-accelerating voltages to ascertain which reflections are most affected by n-beam interactions. When applied to experimental intensity data from 1,2-dihexadecyl-sn-glycerophosphoethanolamine (DHPE), the correction facilitates a direct phase determination based on the probabilistic estimate of three-phase invariants because a more accurate estimate of the hierarchy of |El| values is obtained. When a multisolution technique is used, incorporating algebraic unknowns for certain phase values, the best phase assignment can be assessed by comparison of the single convolution of phased structure factors to the observed structure-factor magnitudes for the low-voltage data. This approach exploits an approximate analogy made earlier by Moodie between the Sayre equation and the phase grating series and is valid as long as the single convolution adequately models experimental low-voltage data (a condition favored by light-atom structures in a low-angle region of reciprocal space). In real space, the correct structure can also be readily identified as the one having the smoothest density profile.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893005394
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    Paper (German National Licenses)
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