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Hi Frank,<br>
<br>
I think it's about where you draw the line... It's very unlikely that
at 3.5A the use of NCS will be a bad idea, and it's very likely that at
1.0A the use of NCS will be a good one. I don't know which side of that
line the cases at around 2A resolution are (I believe the only
systematic and careful study can answer this; or may be someone did it
then I would appreciate a reference), and, as you rightfully pointed
out - the automatic procedures are not perfect, so I usually try both
-:)<br>
<br>
Pavel.<br>
<br>
<br>
On 11/26/2008 3:34 PM, Frank von Delft wrote:
<blockquote cite="mid:492DDD02.6040802@sgc.ox.ac.uk" type="cite">
<pre wrap="">
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">I am refining a structure with a resolution of 2.1 Angstroem using Phenix.
The spacegroup is P 31 2 1 (No. 152) with a twin fraction of 0.37 and twin
law -h,-k,l.
In the refinement procedure the NCS (4 chains) constraints are on, using
individual sites, ADP and occupancy refinement.
</pre>
</blockquote>
<pre wrap="">Just a suggestion to quickly try out... What happens if you turn off the
NCS restraints and do some refinement without using NCS (with and/or
without optimizing the weights)? I know it depends on many factors, but
I've seen a good number of cases at around 2A resolution where the
refinement was better if NCS is not used.
</pre>
</blockquote>
<pre wrap=""><!---->I can't not respond: I've never had a case where *careful* evaluation
and assignment of NCS groups did /not/ allow me to tighten NCS
restraints (without screwing Rfree, of course). But of course, it
requires work: the default procedures aren't good enough yet.
phx
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</pre>
</blockquote>
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