merging equivalent reflections in xplor

Zbyszek Otwinowski zbyszek at mix.swmed.edu
Wed Nov 6 15:21:58 EST 1996


C Squire wrote:
> 
> Hello, I have a question regarding the use of reflection files where
> equivalent reflections have not been merged.
> 
> How will xplor read such a file containing data such as below:
> 
> index -1 0 1   fobs= 99      sigma=5
> index 0 -1 1   fobs= 94      sigma=6
> index 0 1 -1   fobs= 10      sigma=8
> index 1 0 -1   fobs= 15      sigma=7
> 
> The data overall confirms the space group and the above reflections
> are (or should be) equivalent. Other reflections further out in theta
> also show some inconsistencies like this with say 7 equiv. reflections
> all around the same values and with 1 very much smaller and with large sigma.

1.) You should avoid merging fobs, it is better to merge fobs**2 (intensities).
This allows to handle correctly reflections with low ratio of
I/sigma.

2.) Very rarely different observations are exactly on the same scale.
In most cases merging is the last step of scaling procedure.

3.) In example data shown you need to apply rejection of outliers.
In this case I would suspect that 0 1 -1 and 1 0 -1 were obscured
by the beam stop, so they should not be averaged with other data.

-- 
  Zbyszek Otwinowski                     |        zbyszek at chop.swmed.edu
  University of Texas                    |        tel : (214)-648-5098 
  Southwestern Medical Center            |        fax : (214)-648-5095 
  5323 Harry Hines Boulevard  Dallas, Texas  75235-9038
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