>Likelihood and/or the free R-factor offer routes to choose restraint
>weights...
I don't exclude a potential possibility for an efficient, reasonable and
profitable application of even such dirty tricks as soft restraints. Also I'm
sure that a hypothetical opportunity exists for a method of choosing most
robust and safe weights of restraints. Yet all these requisites are not
observed in the current SDPD practice.
>I'm not against constraints, but how do you go about validating somebody
>else's choice of rigid definition?
Validation is a manifold issue similarly complex both for softly-restrained and
for free+constrained refinement. Fortunately, some positive practice has been
developed in the "last ~100 years of crystallography" using rigid-body
fragments.
*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660049, K. Marx 42, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
*******************************************************
________________________________
From: Jonathan WRIGHT <wri...@esrf.fr>
To: s...@yahoogroups.com
Cc: Leonid Solovyov <l_solov...@yahoo.com>; "rietveld_l@ill.fr"
<rietveld_l@ill.fr>
Sent: Wednesday, July 31, 2013 11:36 PM
Subject: Re: [sdpd] Re: Are restraints as good as observations ?
On 31/07/2013 17:25, Leonid Solovyov wrote:
> One can make everything "OK" simply by choosing an "appropriate" weight
> of restraints. The uncertainty in the restraint's weight appropriateness
> makes every restrained refinement a "know how".
Likelihood and/or the free R-factor offer routes to choose restraint
weights, see eg:
http://www-structmed.cimr.cam.ac.uk/Course/Likelihood/likelihood.html#restraints
http://people.cryst.bbk.ac.uk/~tickle/rfree/paper.html
Regardless of the weighting chosen, the weighted difference which comes
back (per restraint) tells you what the data think about the restraint
target value. This information could be deposited along with the fit to
the powder data for all to see.
I'm not against constraints, but how do you go about validating somebody
else's choice of rigid definition?
Cheers,
Jon
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