Kurt
I think that P2/n has no fixed points, and in order to keep the whole
structure from shifting along the c-axis, one of the atoms has to be
arbitrarily fixed. GSAS automatically fixes the first atom z-parameter (was
your atom on the 2-fold symmetry axis?). I remember this from refining
Sorry if I recall what has been discussed before, but I cannot find
it in the archives. I don't use apparantly the proper search terms.
Try this in the old archive (90 emails !) :
http://sdpd.univ-lemans.fr/cgi-bin/searchrietveld.pl?Range=AllFormat=StandardTerms=bail+gsas
or this in the new
On 31 Mar 2004 at 11:34, Armel Le Bail wrote:
Try this in the old archive (90 emails !) :
http://sdpd.univ-lemans.fr/cgi-bin/searchrietveld.pl?Range=AllFormat=StandardTerms=bail+gsas
or this in the new archive (54 emails !) :
The ICSD-WWW database on http://icsdweb.fiz-karlsruhe.de/ or http://icsd.ill.fr/ has
been updated to 76,480 inorganic structures for licensed users, with now over 6000 new
entries being added each year. Unlicensed users have full-feature access to a demo
3000+ structure database.
Notes and
Armel will be pleased to know that the PHP-MySQL server software is
available as open source (but copyright) code from
http://icsd.ill.fr/icsd/install/
Not enough Alan, I want not only the butter but also the
money for the butter. The complete stuff fully open.
500 more CIFs in COD that week,
At 15:56 31/03/2004, Armel Le Bail wrote:
Not enough Alan, I want not only the butter but also the
money for the butter.
And the milkmaid as well I suppose Armel ?
ICSD also contains papers from the American Mineralogist, and even provides direct
links to the original paper in electronic
Arie,
Your suggestion is the best way to handle this. Just sort the data by hkl to put Ka1
with Ka2 and then sum them pairwise. Some day I'll put that into REFLIST, but you can
do that with the help of the MS-DOS comand sort (it is still there in the console
for Win 2K, XP, etc.).
Bob
Dear Stephen ( others),
I know there have been a number of replies to this since P2/n does have an inversion
center which is positioned at the unit cell origin. However, if the space group is Pn
(or P2) then the location of the origin is arbitrary on one or more axes. GSAS does
automatically
[EMAIL PROTECTED] wrote:
Dear Rietvelders,
I used GSAS to refine my structure in P2/n, however the program automatically
fixed the the XYZ positions of the first atom during refinement. To my
surprise, this atom is not seen in the fixed atom list in the atom parameters
menu of GSAS.
Bob,
Thank you for the clarification. I never had doubts that GSAS handles fixed origin
issue properly but also never understand how it
is done. This way has one big advantage over user fixed origin -- it yields standard
uncertainties for all atoms and therefore for
all distances, etc.
Peter
Dear Peter,
the most correct constraint would be to fix a sum of coordinates
of all atoms along polar axis, but not only of the first two.
It gives the best estimation of the standard uncertainties.
Yaroslav Filinchuk
PZ Bob,
PZ Thank you for the clarification. I never had doubts
Peter Zavalij wrote:
Bob,
Thank you for the clarification. I never had doubts that GSAS handles fixed origin
issue properly but also never understand how it
is done. This way has one big advantage over user fixed origin -- it yields standard
uncertainties for all atoms and therefore for
Obviously. I was talking about fixing the origin when it is not fixed by symmetry.
By the way, GSAS when generate symmetry from space group symbol provide information
about the origin.
If the origin is not fixed by symmetry is it clearly stated:
For example for P2 The location of the origin is
Yes, but the atom doesn't have to sit there, unlike in the case of 2/m. So,
GSAS has to fix z for one atom...
I don't have my International Tables with me, please correct me if I'm wrong
(there should be no sites with a fixed z parameter in P2/n).
- Kurt
---
Kurt
This problem can actually quite simply be solved without tables:
There is the old rule (which crystrallographers a definitely able to
prove) to obtain the crystal class:
1.delete the Bravais type symbol (delete P in case of P2/n)
2.substitute screw axes by the correspondingly oriented simple
Sorry Allen - I guess this new generation of crystallographers really is as
bad as you think!
- Kurt
---
Kurt Leinenweber
Department of Chemistry
Arizona State University
Tempe, AZ 85287-1604
Phone: (480)-965-8853
Fax: (480)-965-2747
---
-Original
Thanks
Andreas. I realized I was wrong when I drew a picture of how the glide
plane and the 2-fold axis interact with the translational symmetry. They
make 4 points at +x +y +z, -x -y +z, +x +y -z, -x -y -z (2 pairs definitely
related by a center of symmetry). I should have done that before
I am amazed by the flow of miss information that flows on this list whenever an
apparent problem with a space group comes up.
I asked a related question on sci.techniques.xtallography a few weeks
ago, but have yet to hear anything, misinformation or otherwise. If
anyone here can give me some
Hi Jon,
A lot of what you'll need is in the back of the International Tables Vol. A
in Chapter 15 which goes under the snappy title of Euclidean and affine
normalisers of space groups and their use in crystallography. From memory,
earlier incarnations of Vol. A do not have this chapter.
Bill
Bill,
Thanks! Exactly what I was after and I'd never have guessed it from the
title...
Jon
On Wed, 31 Mar 2004, David, WIF (Bill) wrote:
Hi Jon,
A lot of what you'll need is in the back of the International Tables Vol. A
in Chapter 15 which goes under the snappy title of Euclidean and
I'm just good at guessing!
See you end of April en France.
Bill
-Original Message-
From: Jonathan Wright [mailto:[EMAIL PROTECTED]
Sent: 31 March 2004 23:05
To: [EMAIL PROTECTED]
Bill,
Thanks! Exactly what I was after and I'd never have guessed it from the
title...
Jon
On Wed,
Apologies for sending the personal note to Jon to the whole mailing list -
at least it didn't have gigabytes of attachments - and for the English and
American members of the mailing list, 'en' is not a spelling mistake!
Bill
-Original Message-
From: Jonathan Wright [mailto:[EMAIL
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