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Revision as of 10:06, 12 February 2021
, 10:06, 12 February 2021→Space group selected by XDS: ambiguous with respect to enantiomorph and screw axes
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 that space 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).
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: 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.
