Chapter

Refinement of crystal structures

David Watkin

in Crystal Structure Analysis

Second edition

Published in print June 2009 | ISBN: 9780199219469
Published online September 2009 | e-ISBN: 9780191722516 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199219469.003.0013

Series: International Union of Crystallography Texts on Crystallography

Refinement of crystal structures

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This chapter gives practical examples of structure refinement in crystallography. The fundamental equations are given, particularly for structure factors calculated from an atomic model of the structure. The purposes of refinement are discussed, with reference to problems that may be encountered when carrying it out, including the limitations imposed by the data quality and resolution. The impact of some reflections on particular parameters is leverage and needs to be assessed. Weak reflections may have important information content. Weights and standard uncertainties have to be handled correctly, as must systematic trends in R values or other indicators as a function of Bragg angle, intensity, or other variables. The merits of different kinds of refinement (e.g., F versus F2) are examined. Tools for handling difficult refinements include constraints, restraints, the selection of appropriate parameters and their definition. Incorrect or pseudo-symmetry can strongly affect refinement.

Keywords: refinement; parameters; data; resolution; leverage; weights; systematic trends; constraints; restraints; pseudo-symmetry

Chapter.  7358 words.  Illustrated.

Subjects: Crystallography

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