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Space group determination: Difference between revisions
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Even in case the space group selected by XDS should be incorrect, the resulting list (in CORRECT.LP) should give the user enough information to pick the correct space group herself. She may then put suitable lines with SPACE_GROUP_NUMBER=, UNIT_CELL_CONSTANTS= into XDS.INP and re-run the CORRECT step to obtain the desired result. (The REIDX= line is no longer required; XDS figures the matrix out.) | Even in case the space group selected by XDS should be incorrect, the resulting list (in CORRECT.LP) should give the user enough information to pick the correct space group herself. She may then put suitable lines with SPACE_GROUP_NUMBER=, UNIT_CELL_CONSTANTS= into XDS.INP and re-run the CORRECT step to obtain the desired result. (The REIDX= line is no longer required; XDS figures the matrix out.) | ||
== | == Influencing the selection by XDS == | ||
=== new parameters === | |||
The automatic choice is influenced by a number of decision constants that may be put into XDS.INP but which have defaults as indicated below: | The automatic choice is influenced by a number of decision constants that may be put into XDS.INP but which have defaults as indicated below: | ||
* MAX_CELL_AXIS_ERROR= 0.03 ! relative deviation of unconstrained cell axes from those constrained by lattice symmetry | * MAX_CELL_AXIS_ERROR= 0.03 ! relative deviation of unconstrained cell axes from those constrained by lattice symmetry | ||
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The user may experiment with adjusting these values to make the automatic mode of space group determination more successful. However, it is much easier to just input the space group and cell parameters that the user thinks are correct. | The user may experiment with adjusting these values to make the automatic mode of space group determination more successful. However, it is much easier to just input the space group and cell parameters that the user thinks are correct. | ||
=== alternative indexing === | |||
As the old REIDX= input has lost its importance, it is useful to keep in mind that there are two ways to have XDS choose an indexing consistent with some other dataset: | |||
* using REFERENCE_DATA_SET | |||
* using UNIT_CELL_A-AXIS=, UNIT_CELL_B-AXIS=, UNIT_CELL_C-AXIS= from a previous data collection run with the same crystal (see http://www.mpimf-heidelberg.mpg.de/~kabsch/xds/html_doc/xds_parameters.html#UNIT_CELL_A-AXIS=) | |||
== Screw axes == | == Screw axes == | ||