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Resolution as an indicator of data completeness

  • To: bm@iucr.org
  • Subject: Resolution as an indicator of data completeness
  • From: "George M. Sheldrick" <gsheldr@shelx.uni-ac.gwdg.de>
  • Date: Tue, 09 Dec 1997 18:48:54 +0100
Dear Brian

I agree with Howard's comments that the treatment of Friedel opposites
should be clarified.  I would also like to repeat a further suggestion
that I made in D71.1 (discussing the Acta 97 instructions for authors)
that it is illogical to define: 

data_diffrn_measured_fraction_theta_full
data_diffrn_measured_fraction_theta_max

and

data_diffrn_reflns_theta_full

using the Bragg angle 'theta' rather than the resolution in Angstroms
(which is how a protein crystallographer would have defined it). 
Whereas the resolution gives an immediate indication of the extent of
the data (and hence the data to parameter ratio), theta depends on the
wavelength, which with increasing use of synchrotron data may be
different for different experiments.  Indeed for Laue data the
wavelength is different for each reflection and so 'theta' is useless
whereas 'resolution' would still be sensible.

Will COMCIFS be allowed to preview the 1998 Acta Cryst. instructions for
authors ?!  It might help to prevent accidents.

Best wishes, George

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