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Space group determination: Difference between revisions
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→Subgroup and supergroup relations of these space groups: add reference to ITC Vol A figure
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! Bravais type | ! Bravais type | ||
! spacegroup <br> number <br> suggested by <br> CORRECT | ! spacegroup <br> number <br> suggested by <br> CORRECT | ||
! other possibilities ( | ! other possibilities (with screw axes) | ||
! alternative indexing <br> possible? | ! alternative indexing <br> possible? | ||
! choosing among all spacegroup possibilities | ! choosing among all spacegroup possibilities | ||
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Alternative indexing possibilities taken from http://www.ccp4.ac.uk/html/reindexing.html (for R3 and R32, obverse/reverse are specified). | Alternative indexing possibilities taken from http://www.ccp4.ac.uk/html/reindexing.html (better readable at http://www.csb.yale.edu/userguides/datamanip/ccp4/ccp4i/help/modules/appendices/reindexing.html) (for R3 and R32, obverse/reverse are specified). | ||
If you find an error in the table please send an email to kay dot diederichs at uni-konstanz dot de ! | If you find an error in the table please send an email to kay dot diederichs at uni-konstanz dot de ! | ||
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|- | |- | ||
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[[File:Spacegroups tree2a.png|800px]] | |||
(compare International Tables for Crystallography Vol A (2006), figure 10.1.3.2) | |||
== Space group selected by XDS: ambiguous with respect to enantiomorph and screw axes == | == Space group selected by XDS: ambiguous with respect to enantiomorph and screw axes == | ||
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In case of a crystal with an unknown space group (SPACE_GROUP_NUMBER=0 in [[XDS.INP]]), XDS (since [http://xds.mpimf-heidelberg.mpg.de/html_doc/Release_Notes.html version June 2008]) helps the user in determination of the correct space group, by suggesting possible space groups compatible with the Laue symmetry and Bravais type of the data, and by calculating the R<sub>meas</sub> for these space groups. | In case of a crystal with an unknown space group (SPACE_GROUP_NUMBER=0 in [[XDS.INP]]), XDS (since [http://xds.mpimf-heidelberg.mpg.de/html_doc/Release_Notes.html version June 2008]) helps the user in determination of the correct space group, by suggesting possible space groups compatible with the Laue symmetry and Bravais type of the data, and by calculating the R<sub>meas</sub> for these space groups. | ||
XDS (or rather, the [[CORRECT.LP|CORRECT]] step) makes an attempt to pick the correct space group automatically: it chooses | XDS (or rather, the [[CORRECT.LP|CORRECT]] step) makes an attempt to pick the correct space group automatically: it chooses the space group (or rather: Laue point group) which has the highest symmetry (thus yielding the lowest number of unique reflections) and still a tolerable R<sub>meas</sub> compared to the R<sub>meas</sub> the data have in any space group (which is most likely a low-symmetry space group - often P1). | ||
In some cases the automatic choice is the correct one, and re-running the [[CORRECT.LP|CORRECT]] step is then not necessary. However, neither the correct enantiomorph nor [[Space_group_determination#Screw_axes|screw axes]] (see below) are determined automatically by XDS. | In some cases the automatic choice is the correct one, and re-running the [[CORRECT.LP|CORRECT]] step is then not necessary. However, neither the correct enantiomorph nor [[Space_group_determination#Screw_axes|screw axes]] (see below) are determined automatically by XDS. [[Pointless]] is a very good program (usually better than CORRECT) to suggest possible space group (and alternatives). See also [[Space_group_determination#Notes|Notes]], and [[Space_group_determination#checking_the_CORRECT_assignment_with_pointless|checking the CORRECT assignment with pointless]] (below). | ||
== Space group selected by user == | == Space group selected by user == | ||