[Wien] question about sgroup

[georg at chem.au.dk]

If you look at the symm. ops. in int. tab. then there are 24 and then the same
24  with an added 1/2 in two directions and so on.

International tables thus includes the F-centering among its symmetry operators.
Wien doesn't, this is set in the lattice type: hence the factor of 4.

 Georg

Quoting Fred Nastos <nastos at physics.utoronto.ca>:

> Hi,
> 
> In some cases it seems like sgroup does not provide all the space
> group symmetry operations.  It seems to provide all the rotations
> (proper and improper), but does not seem to provide all 
> rotations+translations.  I think my question/misunderstanding is
> most easliy conveyed through an example.
> 
> Consider the two systems: zincblende and wurtzite.  Let's assume
> we have a struct file for each case: zincblende.struct and wurtzite.struct.
> 
> If I run 'x sgroup' for the wurtzite case, sgroup finds that the structure
> belongs to spacegroup 186, and the file wurtzite.struct_sgroup
> has 12 symmetry matrices appended at the end of the file.  Those
> 12 matrices are the same as what one finds at the website:
> 	http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-getgen
> under spacegroup 186.
> 
> Of these 12 symmetry operations, six of them are the point group
> operations, and the other six are rotations+translations.  It seems
> like sgroup provides the user with all the space group symmetry
> matrices.
> 
> But, if I run 'x sgroup' for the zincblende case, sgroup finds that the
> structure belongs to space group 216, and it lists 24 symmetry matrices
> at the end of zincblende.struct_sgroup.  But space group 216, according
> to the above site, has 96 space group symmetry operations (the product
> of 24 point group operations and four different trasnlation vectors).  So, 
> there appears to be a contradiction.
> 
> Thank you for your time.
> 
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-- 
Georg Madsen
Department of Chemistry
Aarhus University
DK-8000 Århus C
Denmark
tlf (+45) 89423885