I'm most interested in how to interpret the x1,x2,x3,x4,... algebra as
symmetry operations. All I did (admittedly just a guess) was to ignore
anything after x3 and make x1=x, x2=y, x3=z. (At least it reported the
correct space group as calculated from the operators!)
But I could be totally incorrect in doing that, and while the structure
looked pretty good, it's not right. I guess I don't see how that
information is supposed to be used as a basis for a structural description.
Looks very interesting, though, and I really would like to do something
creative with that. So if you have any idea, Brian, do let me know.
Yes, these were in Acta Cryst B. (Good call, Brian!) They came from
supplemental material collected by Peter Murray-Rust at
http://crystaleye.ch.cam.ac.uk/search/?search_provider=structure&sys_name=&smiles=[Al]&inchi=&inchi_key=&submit=search(that
server may not respond sometimes, I think)
_space_group_ssg_name Imma(00\g)s00
_journal_name_full 'Acta Crystallographica, Section B'
_journal_year 2008
_journal_volume 64
_journal_issue 4
_journal_page_first 417
_journal_page_last 425
_journal_paper_category FA
_journal_coeditor_code SN5068
_publ_contact_author_name 'Lazic, Biljana'
Bob
On Tue, Sep 4, 2012 at 11:40 AM, Brian McMahon <[email protected]> wrote:
> Thanks, Pat.
>
> A useful document to read alongside the CIF dictionary is the
> Checklist published by the Commission on Aperiodic Crystals in
> Acta Cryst. (1997), A53, 95-100.
> (http://dx.doi.org/10.1107/S0108767396010185)
>
> There is not much software that currently writes CIFs for modulated
> structures (though we do have a number as supplementary files
> deposited mostly with Acta Cryst. B).
>
> Bob: If you're interesting in looking into this further, I can send
> you off-list a few more pieces of relevant documentation and try
> to connect you up with the experts in superspace group operators
> and modulated structure determination. I don't know what tools,
> if any, already exist for visualising such structures, but it might
> be very interesting to investigate further.
>
> Regards
> Brian
> _________________________________________________________________________
> Brian McMahon tel: +44 1244 342878
> Research and Development Officer fax: +44 1244 314888
> International Union of Crystallography e-mail: [email protected]
> 5 Abbey Square, Chester CH1 2HU, England
>
> On Tue, Sep 04, 2012 at 12:11:26PM -0400, Pat Carroll wrote:
> > Bob,
> >
> > These CIF items have to do with "modulated structures". I only
> have a
> > "nodding acquaintance" with this concept, but I know these CIF items
> > would not appear in a "normal" CIF. Is it only one, particular CIF
> > that is giving that error? Then it must be one modulated structure
> > that you have a CIF for.
> >
> > Here is a link to an IUCR definition of modulated structure:
> >
> > http://reference.iucr.org/dictionary/Modulated_crystal_structure
> >
> > And here is a link to the CIF items for modulated structures:
> >
> > http://www.iucr.org/__data/iucr/cifdic_html/1/cif_ms.dic/index.html
> >
> >
> > Pat
> >
> > Patrick J. Carroll, Ph.D.
> > Director, X-ray Crystallography Facility
> > Department of Chemistry
> > University of Pennsylvania
> > Philadelphia, PA
> >
> > Phone: 215-898-3505
> > Web: http://macxray.chem.upenn.edu
>
>
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--
Robert M. Hanson
Larson-Anderson Professor of Chemistry
Chair, Chemistry Department
St. Olaf College
Northfield, MN
http://www.stolaf.edu/people/hansonr
If nature does not answer first what we want,
it is better to take what answer we get.
-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
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