[phenixbb] increasing NCS restraints

Dale Tronrud det102 at uoxray.uoregon.edu
Thu Oct 17 12:57:28 PDT 2013

   I'm puzzled.  Didn't you say that the translation of your ncs
two-fold was not equal to half the "a" cell edge?  If it is not
a translation of 1/2 (in fractional coordinates) then it cannot
be a crystallographic symmetry element and your space group cannot
be P212121.  Unless this condition is met, the similarity of your
molecules is unimportant.

Dale Tronrud

On 10/17/2013 12:48 PM, Yarrow Madrona wrote:
> I am doing restrained NCS refinement and would like to know how to set the
> target weight of the cartesian restraint in the command line? I also found
> a sigma value in the GUI. I read that I can decrease it in order to
> increase the NCS restraints. However, I have seen this under Torsional
> restraints. Does this also apply to cartesian restraints?
> I am doing this so that I can look at the differences in position and
> B-factors of two molecules in the ASU that I am trying to determine are
> related by a perfect or imperfect 2(1) screw axis. (I posted a question
> about this on the CCP4 bullitan board.) If the values between molecules
> are exactly the same then presumably the space group is actually P212121
> with 1molecule in the asu instead of P21 with two molecules. I already
> know that the P21 dimer superimposes almost exactly on the P212121 monomer
> and it's symmetry mate. I just don't know how "perfectly" they align and I
> am hoping this approach will tell me. I hope this makes some sense.
> -Yarrow

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