[phenixbb] R free assignment in thin shells

Tim Gruene tg at shelx.uni-ac.gwdg.de
Thu Jun 4 00:21:49 PDT 2015

Dear mohamed noor,

thin shells are commonly picked in cases of twinned data. As Andrew
points out in the email you link, the NCS makes the refinement behave
well, so also you will probably get away with 'normal' randomly selected

At high resolution the data to parameter refinement also increases and
the Rfree looses its meaning. That's one of the reasons why people don't
use Rfree for small molecule structure determination and why ML
refinement show not much improvement compared to least squares
minimisation (it's different for charge density studies, when the data
to parameter goes down again).


On 06/04/2015 01:18 AM, mohamed noor wrote:
> Dear all
> I found a not-so-old thread about this topic:
> http://phenix-online.org/pipermail/phenixbb/2012-January/018259.html. Maybe
> there has been significant changes in phenix.refine since then.
> However, I couldn't find a conclusion. In my case, my data extends to 1.4 A
> with the R/R free being around 23/26 %. There is also pseudo symmetry, so
> there are 16 NCS copies in a lower symmetry group than what Xtriage
> suggested. The map looks fine with density for some H atoms even being
> visible.
> On what basis should I decide whether to use (or not) thin shell
> assignment? And what is the cut-off for number of NCS copies?
> Thanks.
> _______________________________________________
> phenixbb mailing list
> phenixbb at phenix-online.org
> http://phenix-online.org/mailman/listinfo/phenixbb
> Unsubscribe: phenixbb-leave at phenix-online.org

Dr Tim Gruene
Institut fuer anorganische Chemie
Tammannstr. 4
D-37077 Goettingen
phone: +49 (0)551 39 22149


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 173 bytes
Desc: OpenPGP digital signature
URL: <http://phenix-online.org/pipermail/phenixbb/attachments/20150604/3e1308b5/attachment.sig>

More information about the phenixbb mailing list