Refinement with twinned data question

From: Yuri
Date: 2 October 2011 03:27
Dear all,
I have some questions about the correct protocol for refinement of twinned data (0.46)

1- How do I ensure that my Rfree set is generated properly?

2-I noticed that if I enable intensity based twin refinement, refmac estimates the correct twin fraction
law -h,-k,h+l. But for subsequent refinement rounds should I keep using the raw intensity mtz file or
the newly generated mtz with PHIC and FOM information?

Thank you
--
Yuri Pompeu

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From: Garib N Murshudov

Dear Yuri

1) For twin refinement refmac internally changes free reflections so that twin related reflections belong to the same class (twin or working). However it would be good to generate free reflections in higher space group that would include twin and space group symmetries. 

2) You should always use original data for refinement. Never use output from refmac for next round of refinement. Output mtz file is representation of model.

regards

Garib

Garib N Murshudov
Structural Studies Division

MRC Laboratory of Molecular Biology

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From: Yuri

1-So for my case, I should try and generate Rfree flags, in the higher apparent C 2 2 21  and not the real P 1 21 1, correct?
2-I noticed that if I used the output PHIC FOM data, the maps looked awesome! Too good almost...
Thanks a lot

--  Yuri Pompeu