I guess the point is to "know thy data", to avoid problems down the
track: a statistical test for twinning forms one of a battery of tests
which can be performed independently of a coordinate set (Matthews
coefficient, self-RF, etc.), and with relative ease. Importantly, in
the case of partial
I second Kay's observation. Mine were lovely single looking crystals in
P3 but had a twin fraction that varied from 0-0.5 from crystal to crystal.
If anyone is still following this thread, I have a question for the
lattice jocks out there:
I once had a crystal in P3121 which routinely diffracte
This usually leads to a mad
chase through all possible space groups, twinning refinements, etc. and,
in my experience, often results in a lot of time being spent for no
significant improvements.
If one has a model to refine, it is actually very straightforward to
test all possible merohedral
Hi,
I think a problem I've had with my thesis project applies to this discussion:
My Rfactors, after having built a reasonable model into experimental maps in
P3121, were stuck in the upper 40s, and would absolutely not go lower. Trying
the other space group options (P31, C2) didn't help, and t
oops didn't read that first one...
but from my own experience, twin refinement can lead to significant
improvements (10 percent drop in R-factors)
--
"Feel free" - 5 GB Mailbox, 50 FreeSMS/Monat ...
Jetzt GMX ProMail testen: www.gmx.net/de/go/mailfooter/promail-out
Dear Eleanor et al:
mmtbx.xtriage, which is part of the full-blown ccp4 install, and
phenix.xtriage, which I think is basically the same thing, are also
options, and run a variety of twinning and other sanity checks.
mmtbx.xtriage --help tells how to run it, fairly painlessly.
All the best,
B
maybe interesting literature concerning this topic:
Lebedev AA, Vagin AA, Murshudov GN
Intensity statistics in twinned crystals with examples from the PDB.
Acta Crystallogr D Biol Crystallogr. 2006 Jan;62(Pt 1):83-95.
--
Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen!
Ideal f
-
It's very possible with any overlap of lattice points, even in the lower
symmetry space groups. To extend Eleanor's list: For example, I once had a
structure with the unit cell relationship 3c cos(beta) = -a. In cases like
that, it's not really a c
It's very possible with any overlap of lattice points, even in the lower
symmetry space groups. To extend Eleanor's list: For example, I once had a
structure with the unit cell relationship 3c cos(beta) = -a. In cases like
that, it's not really a clean diffraction, but looks very much like a
single
There are many and various reasons for unpleasantly high R values, and
twinning is undoubtedly one of them.
But you can only have twinning with apparently good diffraction if the
cell dimensions allow it.
It is always a possibility in trigonal, tetragonal and cubic cells.
Certain other comb
Hi Sue,
This reference has very useful info
Lebedev AA, Vagin AA, Murshudov GN.
Intensity statistics in twinned crystals with examples from the PDB.
Acta Crystallogr D Biol Crystallogr. 2006 Jan;62(Pt 1):83-95. Epub
2005 Dec 14.
PMID: 16369097 [PubMed - indexed for MEDLINE]
Roberto
On 21
Sue Roberts wrote:
Hello
A partially philosophical, partially pragmatic question.
I've noticed a trend, both on ccp4bb and locally, to jump to twinning as
an explanation for data sets which do not refine well - that is data
sets with R and Rfree stuck above whatever the person's pre-conceived
Hello
A partially philosophical, partially pragmatic question.
I've noticed a trend, both on ccp4bb and locally, to jump to twinning
as an explanation for data sets which do not refine well - that is
data sets with R and Rfree stuck above whatever the person's pre-
conceived idea of an acce
13 matches
Mail list logo
