>Instead,
I adopted the restraint/constraint system as soon as some
>distances
went stranges.
>Yes,
fear, fear to be personnally attacked again that way.
For me
restraints are much more frightful ;-(:
http://www.google.com/search?q=restraints
While for
some sort of people they may be thrilling.
>The problem with powder diffraction measurements
> is that they often leave us information-starved.
Certain informational starvation is a feature of any experimental technique and
powder diffraction is not a marginal one in this respect. Starvation, however,
is not an absolution for artificial
>All Rietvelders (included me) are certainly trying
> a completely free refinement before to decide or
> not to use selected restraints.
About "All" I certainly doubt.
>Am I especially scrutinized? I feel more and more
>uncomfortable about such verifications of everything I do:
I believe that o
>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 c
A colleague asks if anyone can help him with the rotating sample
compartment of an old Philips 1055/81 goniometer ? He badly needs this
part since the company (Panalytical) say they no longer support this
very old system.
__
Dr Alan Hewat, NeutronOptics,
On 31/07/2013 20:19, Brian Toby wrote:
To perform R-free with powder data, one must excise multiple complete
peaks from the pattern, say a few sections making up 10-20% of
pattern.
Hi Brian,
It is not so bad, you only need to throw in some peak intensities as
variables (a partial Pawley). You
Let me pontificate a bit on restraints and on R-free etc.
The problem with powder diffraction measurements is that they often leave us
information-starved. We just don't get enough data to investigate what we want
to learn from the experiment, along with all the things we [think we] already
kn
>The problem of having jammed the wrong molecule
> into a unit cell can be identified by restraints which
> are violated. With rigid bodies it is more difficult to
> find out what the data are trying to tell you. Is this
>wrong molecule issue the problem you fear?
I prefer resolving such proble
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
LANSCE School on Neutron Scattering
Geosciences & Materials in Extreme Environments
http://lansce.lanl.gov/neutronschool
October 16-25, 2013
Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos New
Mexico
The 2013 LANSCE School on Neutron Scattering will focus on outstandin
>input restraint: C(sp3) to C(sp3) distance ~ 1.54
>output distance: 1.54 -> OK
>output distance: 1.4x -> Could it be sp2-sp2 or a wrong atom assignment?
One can make everything "OK" simply by choosing an "appropriate" weight of
restraints. The uncertainty in the restraint's weight appropriatenes
On 31/07/2013 03:07, Leonid Solovyov wrote:
... There is a
widely scattered belief that restraints always improve not only the
restrained values, but also the “unrestrained” part of structure such as
intermolecular distances, orientations, planarity etc.
Apart from your word "always", I certai
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