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 Message-----
From: Allen Larson [mailto:[EMAIL PROTECTED]
Sent: Wednesday, March 31, 2004 9:33 AM
To: [EMAIL PROTECTED]
[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.
>
> Please advise and many thanks,
>
> stephen
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 am forced to wonder if the
correspondents in these exchanges have ever looked at 'The International
Tables,
Volume A(1983)' or Volume 1(1969) or the earlier volume which dates in the
1930's. Or any of the several other treatises that can also serve as a
source
for this information.
The GSAS package contains a program, SpcGroup, that can be used to list the
symmetry operations of any possible string defining a possible space group.
In
general the space group symbol consists of 2 or more groups of characters
delimited by spaces. Please note that the spaces separating axial operations
are
required in the GSAS interpretation of the space group symbol. Thus 'R3c'
must
be written as 'R 3 c' or taking advantage of the fact that the lattice type
can
only occupy one character, 'R3 c', is accepted, but not recommended.
I might also note that all of this is based on the use of keyboards in
general
use in English speaking countries. And I did have no information concerning
what
you might get using other keyboards.
Now for P2/n is a centric space group for which there, in my mind, there
exists
no reasonable origin choice that the 1bar site. Therefore the software would
always choose that for the origin of the unit cell.
Allen C. Larson
