[Wien] Partial Occupancy/Origin Shift

[Dr. Sharat Chandra]

Dear Travis

The conventional positions for the 152 spgr are:

Multiplicity Wyckoff  Site      Coordinates
             letter   symmetry 
 
6 c  1	(x,y,z),(-y,x-y,z+1/3),(-x+y,-x,z+2/3),(y,x,-z),
	(x-y,-y,-z+2/3),(-x,-x+y,-z+1/3)  
3 b .2.	(x,0,5/6),(0,x,0.16667),(-x,-x,1/2)  
3 a .2.	(x,0,1/3),(0,x,2/3),(-x,-x,0)

When shifted by 0.5,0.5,0.5, these yield

6 c  1	(x-1/2,y-1/2,z-1/2),(-y-1/2,x-y-1/2,z-0.16667),  
	(-x+y-1/2,-x-1/2,z-0.16667),(y-1/2,x-1/2,-z-1/2),  
	(x-y-1/2,-y-1/2,-z-0.16667),(-x-1/2,-x+y-1/2,-z-0.16667)  
3 b .2.	(x-1/2,-1/2,1/3),(-1/2,x-1/2,2/3),(-x-1/2,-x-1/2,1)  
3 a .2.	(x-1/2,-1/2,-0.16667),(-1/2,x-1/2,+0.16667),(-x-1/2,-x-1/2,1/2)  

And, when shifted by 0,0,1/3

6 c  1	(x,y,z-1/3),(-y,x-y,z),(-x+y,-x,z+1/3),(y,x,-z-1/3),  
	(x-y,-y,-z+1/3),(-x,-x+y,-z) 
3 b .2.	(x,0,0.5),(0,x,0.83333),(-x,-x,0.16667)
3 a .2.	(x,0,0),(0,x,1/3),(-x,-x,2/3) 


As you can see there is not much change except that the coordinates have
been reduced by 0.5,0.5,0.5 or 0,0,1/3 everywhere. In this sense, there
should not be any difference in the band structures you calculate with the
shifted and unshifted coordinates. If you want more information, please
visit the site http://www.cryst.ehu.es/cryst/get_wp.html for finding out
the general coordinates and Wyckoff positions of the space groups.
 
Hope this solves the proble.

Regards
Sharat

On Sun, 27 Feb 2005, Travis Sefzik wrote:

> Xavier,
> 
> Thanks again for the help.
> 
> The problem stems from a paper by Jurgen Glinnemann in '92 (Z 
> KRISTALLOGR 198 (3-4): 177-212 1992).  He had reported structures of 
> high pressure GeO2 (however using spc.gr. 152 and origin shift of 1/3c 
> contrary to what Sowa (Z KRISTALLOGR 184: 257-268 1988)had done 
> previously).  I was really hoping to use these structures but have 
> never taken the time to work through the math within crystallography.
> 
> I have a plan that will hopefully keep me from further investigating 
> the intricacies of crystallography ... but it would be great to plug 
> Glinnemann's numbers into WIEN directly.