[ccp4bb]: Can P43212 and P41212 be distinguished by anomalous signals?

[Phil Evans <pre@mrc-lmb.cam.ac.uk>]

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Q. Steven Xu writes:
 > 
 > My another questions is, once I determine the space group, do I need to
 > flip the sites and try both possibilites? I remember somebody asked the
 > similar question before, but just can not find a clue in the archive.
 > sorry about that. Thanks in advance.
 > 

Flipping the sites & changing the spacegroup always go together

The easiest way to think about this is to consider inverting all the
sites in the whole cell (not just the asymmetric unit). This
automatically converts a 4(1) into a 4(3)

eg

1) in P4(1)
sites at x,y,z :  -y, x, 1/4+z

2) Invert to -x,-y,-z:  y, -x, 3/4-z
   substitute p=-x, q=-y,r=-z

sites at p,q,r: -q,p,3/4+r

  these are related by a 4(3) axis, ie the spacegroup is now P4(3)

Phil