Nat Echols wrote:
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Thanks to all who replied to my indexing question; I think I have the
problem sort of figured out now. Either I get better crystals, or I
try refining in a large P21 cell. (Hopefully the former.)
If I'm stuck in P21, I have four molecules in the ASU, which are
almost exactly crystallographically related. I've been warned that NCS
in these cases risks essentially cross-refining the Rfree set. I've
also seen reference to picking an Rfree set carefully to avoid this. I
guess picking thin resolution shells was the old way, but I also saw a
reference to SFTOOLS doing something more precise and picking specific
refletions that would be related by my NCS operators. Or something
like that. Can anyone explain this further?
I try to make sure the pseudo-symmetry related reflections have the same
freer flag. I do this by indexing and assigning FeeRflags to the highest
pseudo symmetry.
expanding the data to P1 - that generates n identical copies of the
FreeRflag
Then reindex that expanded data into the P21 indexing.
Then add the FreeRfalg only from that reindexed P1 set to your P21 data!
Clear???
Eleanor
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