Optimisation

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General guidelines for obtaining a good result from XDS


Final polishing

  • After running through all steps of XDS (including space group determination), one might want to
cp GXPARM.XDS XPARM.XDS
mv CORRECT.LP CORRECT.LP.old
grep -v REIDX XDS.INP > XDS.INP.new
mv XDS.INP.new XDS.INP

and re-run the INTEGRATE and CORRECT steps. This has the advantage that the refined geometry parameters (from CORRECT) are recycled into INTEGRATE, which sometimes leads to better R-factors.

  • look through the list of reflections labeled as "aliens" in CORRECT.LP. Decide whether they follow a slowly decaying non-Wilson distribution (resulting in many reflections with Z > 8 instead of none in the case of a perfect Wilson distribution), or whether the top ones are true outliers. The latter occurs most often from ice reflections (these may even be there when no ice rings are visible). My personal rule of thumb is that when the integer parts of Z cover the numbers 8, 9, ... n, but there are no reflections with Z = n+1, then I consider all reflections with Z > n+1 as outliers. These are then put (i.e. copied) into REMOVE.HKL, and CORRECT is re-run.