You should pick your free-R set in C2221 and then symmetry-expand it to
C2. Otherwise, every hkl in your "free" R set will have an NCS "mate"
in the working set, and using NCS restrains will completely invalidate
the free R analysis. That is, your free-R will be essentially equal to
the regular crystallographic R and it will be possible to take a
completely wrong MR solution and refine it to an "acceptable" free R,
and if you do that, we will all make fun of you.
-James Holton
MAD Scientist
Yu Jiang wrote:
Dear all,
I am now refining one structure in space group C2 with 2 molecules,
however we find the data can be processed in C2221 with 1 molecule.
The questions are:
1. Can I still use space group C2 instead of C2221, even if the two
molecules almost have crystallographic symmetry? Should I provide any
excuses?
2. Is there any indication or necessity to refine structures in lower
space group instead of higher?
Many thanks!
