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SHELXL: Difference between revisions
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SHELXL provides facilities for refining against data from merohedral, pseudo-merohedral, and non-merohedral twins (Herbst-Irmer & Sheldrick, 1998). Refinement against data from merohedrally twinned crystals is particularly straightforward, requiring only the twin law (a 3x3 matrix) and starting values for the volume fractions of the twin components. Failure to recognize such twinning not only results in high R-factors and poor quality maps, it can also lead to incorrect biochemical conclusions (Luecke, Richter & Lanyi, 1998). Twinning can often be detected by statistical tests (Yeates & Fam, 1999), and it is probably much more widespread in macromolecular crystals than is generally appreciated! | SHELXL provides facilities for refining against data from merohedral, pseudo-merohedral, and non-merohedral twins (Herbst-Irmer & Sheldrick, 1998). Refinement against data from merohedrally twinned crystals is particularly straightforward, requiring only the twin law (a 3x3 matrix) and starting values for the volume fractions of the twin components. Failure to recognize such twinning not only results in high R-factors and poor quality maps, it can also lead to incorrect biochemical conclusions (Luecke, Richter & Lanyi, 1998). Twinning can often be detected by statistical tests (Yeates & Fam, 1999), and it is probably much more widespread in macromolecular crystals than is generally appreciated! | ||
No changes are needed to the .hkl file for merohedral twinning, but the data should be merged in the lower of the two relevant Laue groups). For non-merohedral twinning a special (‘HKLF 5’) format is required.<br> | No changes are needed to the .hkl file for merohedral twinning, but the data should be merged in the lower of the two relevant Laue groups). For non-merohedral twinning a special (‘HKLF 5’) format is required for the intensity data file.<br> | ||
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Sheldrick, G.M. (2008). "A short history of SHELX", ''Acta Crystallogr''. '''D64''', 112-122 [''Standard reference for all SHELX... programs''].<br> | Sheldrick, G.M. (2008). "A short history of SHELX", ''Acta Crystallogr''. '''D64''', 112-122 [''Standard reference for all SHELX... programs''].<br> | ||
Sheldrick, G.M. & Schneider, T.R. (1997). ''Methods Enzymol''. '''277''', 319-343 [Macromolecular refinement with SHELXL]. | Sheldrick, G.M. & Schneider, T.R. (1997). ''Methods Enzymol''. '''277''', 319-343 [''Macromolecular refinement with SHELXL'']. | ||
The following additional sources of information may be found via the SHELX homepage (http://shelx.uni-ac.gwdg.de/SHELX): "SHELX-97 Manual as PDF", "Mini-protein refinement tutorial". "P1-Lysozyme refinement tutorial", "Thomas Schneider's FAQs" and "FAQs: Macromolecules" | The following additional sources of information may be found via the SHELX homepage (http://shelx.uni-ac.gwdg.de/SHELX): "SHELX-97 Manual as PDF", "Mini-protein refinement tutorial". "P1-Lysozyme refinement tutorial", "Thomas Schneider's FAQs" and "FAQs: Macromolecules" | ||