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Some Beq are more equivalent than others

Some Beq are more equivalent than others Crystallographic structural models for macromolecules have typically included an isotropic displacement parameter Biso for each atom. In cases where the structural model instead includes anisotropic displacement parameters Uij, the derived quantity Beq can be substituted for Biso for many purposes. Beq is not, however, the best predictor of the value Biso that would hypothetically have been obtained by direct refinement of an isotropic model. A new entity Best is proposed that represents an estimate for Biso that minimizes the Kullback–Leibler divergence from a paired anisotropic model. In general Best/Beq < 1, with the difference between the two values becoming larger for atoms that are more anisotropic. Although this difference does not affect direct refinement of either isotropic or anisotropic models, it is relevant to any analysis that compares isotropic and anisotropic models of the same underlying structure. In particular, it may lead to improved selection of multi‐group TLS models based on analysis of an initial isotropic refinement. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Crystallographica Section A Foundations of Crystallography Wiley

Some Beq are more equivalent than others

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Publisher
Wiley
Copyright
Copyright © 2011 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0108-7673
eISSN
1600-5724
DOI
10.1107/S0108767311034350
pmid
22011466
Publisher site
See Article on Publisher Site

Abstract

Crystallographic structural models for macromolecules have typically included an isotropic displacement parameter Biso for each atom. In cases where the structural model instead includes anisotropic displacement parameters Uij, the derived quantity Beq can be substituted for Biso for many purposes. Beq is not, however, the best predictor of the value Biso that would hypothetically have been obtained by direct refinement of an isotropic model. A new entity Best is proposed that represents an estimate for Biso that minimizes the Kullback–Leibler divergence from a paired anisotropic model. In general Best/Beq < 1, with the difference between the two values becoming larger for atoms that are more anisotropic. Although this difference does not affect direct refinement of either isotropic or anisotropic models, it is relevant to any analysis that compares isotropic and anisotropic models of the same underlying structure. In particular, it may lead to improved selection of multi‐group TLS models based on analysis of an initial isotropic refinement.

Journal

Acta Crystallographica Section A Foundations of Crystallography – Wiley

Published: Jan 1, 2011

Keywords: ; ;

References