I am refining in phenix twin law h,-k,-h-l.
Without twinning I was around 0.36 Rfree and 0.25 with twinning.
I am noticing however that my Rgap keeps increasing slowly... (little
concerned now its at 8% - 0.18-0.26 - to 2.4A)
Maps look decent for 2.4A I have a lot of clashes however some are just
bad waters though. phenix does not do real space when twinning is
enabled.
Any ideas here?
thank you much
On Thu, 29 Sep 2011 10:25:17 -0400, Phil Jeffrey wrote:
Yuri,
Detwinning relies on having both twin-related reflections present to
calculate either/both of the the de-twinned data values. Therefore
it
magnifies incompleteness depending on where your missing data is with
respect to the twin operator.
I'd recommend against trying to do this with a twin fraction close to
0.5. From the DETWIN docs:
Itrue(h1) = ((1-tf)*iTw(h1) -tf*iTw(h2)) / (1-2tf)
i.e. tf = twin fraction, so 1/(1-2tf) becomes a large number and it's
multiplying a weighted term of the form: (iTw(h1) - iTw(h2)) which
becomes a very small number as the twin fraction approaches 0.5. The
latter difference can easily be less than sigma(I), and so the
signal/noise of your data plummets.
Better to use REFMAC and phenix.refine's abilities to compensate for
the twin fraction directly in refinement and leave your data as it
is.
Phil Jeffrey
Princeton
On 9/29/11 10:03 AM, Yuri Pompeu wrote:
After I ran DETWIN with the estimated 0.46 alpha, my completeness
for the detwinned data is now down to 54%!!!
Is this normal behavior? (I am guessing yes since the lower symmetry
untwinned dat is P1 21 1)
--
Yuri Pompeu
