NDLI: Maximum entropy method and charge flipping, a powerful combination to visualize the true nature of structural disorder from in situ X-ray powder diffraction data.

Content Provider	World Health Organization (WHO)-Global Index Medicus
Author	Samy, Ali Dinnebier, Robert E. Van Smaalen, Sander Jansen, Martin
Description	Country affiliation: Germany Author Affiliation: Samy A ( Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.)
Abstract	In a systematic approach, the ability of the Maximum Entropy Method (MEM) to reconstruct the most probable electron density of highly disordered crystal structures from X-ray powder diffraction data was evaluated. As a case study, the ambient temperature crystal structures of disordered alpha-Rb(2)[C(2)O(4)] and alpha-Rb(2)[CO(3)] and ordered delta-K(2)[C(2)O(4)] were investigated in detail with the aim of revealing the ;true' nature of the apparent disorder. Different combinations of F (based on phased structure factors) and G constraints (based on structure-factor amplitudes) from different sources were applied in MEM calculations. In particular, a new combination of the MEM with the recently developed charge-flipping algorithm with histogram matching for powder diffraction data (pCF) was successfully introduced to avoid the inevitable bias of the phases of the structure-factor amplitudes by the Rietveld model. Completely ab initio electron-density distributions have been obtained with the MEM applied to a combination of structure-factor amplitudes from Le Bail fits with phases derived from pCF. All features of the crystal structures, in particular the disorder of the oxalate and carbonate anions, and the displacements of the cations, are clearly obtained. This approach bears the potential of a fast method of electron-density determination, even for highly disordered materials. All the MEM maps obtained in this work were compared with the MEM map derived from the best Rietveld refined model. In general, the phased observed structure factors obtained from Rietveld refinement (applying F and G constraints) were found to give the closest description of the experimental data and thus lead to the most accurate image of the actual disorder.
File Format	HTM / HTML
ISSN	01087681
e-ISSN	16005740
Journal	Acta Crystallographica Section B Structural Science
Issue Number	Pt 2
Volume Number	66
Language	English
Publisher	Wiley-Blackwell
Publisher Date	2010-04-01
Publisher Place	United States
Access Restriction	Subscribed
Subject Keyword	Discipline Analytical Discipline Chemistry Techniques
Content Type	Text
Resource Type	Article
Subject	Biochemistry, Genetics and Molecular Biology

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