[Wien] Spacegroup issue

[Jorissen Kevin]

In WIEN, a rhombohedral system (ie one with a R space group) is specified with 'R' lattice, hexagonal lattice constants, and rhombohedral atom coordinates.  This is very stupid, but that's the way it is.
 
Kevin.
 

	-----Oorspronkelijk bericht----- 
	Van: Michael Frotscher [mailto:frotscher at chemie.uni-hamburg.de] 
	Verzonden: do 11/13/2003 3:20 
	Aan: wien at zeus.theochem.tuwien.ac.at 
	CC: 
	Onderwerp: [Wien] Spacegroup issue
	
	

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	Hello, WIEN-ML
	
	I'm running into some trouble with WIEN2k when generating a struct-file for
	alpha-rhombohedral boron (Yes, I know there is a example struct-file for this
	but this is somehow completely wrong).
	
	I'm referring to Spacegroup 166 (R-3m), where I have two cell choices: the
	rhombohedral setup or the hexagonal setup. The rhombohedral would seem
	logical as we only have 12 Atoms in the elementary cell. However, when trying
	to generate a struct-file with a=b=c and alpha=beta=gamma!=90° StructGen
	tells me: "cell parameters are not consistent with space group".
	
	The other possibility would be a hexagonal cell with the drawback of a tripled
	cell volume. Structgen accepts the lattice parameters. But the former two
	six-fold atomic positions (totaling to 12 Atoms) now need to be 18-fold
	according to symmetry. Structgen just generates 12-fold atomic positions.
	
	When trying to import cif-files (both rhombohedral and hexagonal ones) I
	always end up with a mixture of hexagonal lattice parameters and rhombohedral
	atom positions.
	
	Sincerely,
	- --
	Michael Frotscher
	Institute of Inorganic and Applied Chemistry
	University of Hamburg, Germany
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