[Wien] Supercell setup

[Peter Blaha]

supercell does not support R lattices.
R lattices span usually a very "lenghty" unit cell. By simply taking some 
multiplicity of the R basis vectors, you would generate a fairly 
1D-system providing eg. a very special "ordering" along one direction, but 
certainly not a good 3D distribution. 
Thus you should think (and visualize) how a supercell would distribute 
your Mn/Ni atoms.
A good beginning is to transfer R into a H lattice (see the Int.Tables of 
Cryst. for details). This is already a 3 times 
larger unit cell and probably a better start for a supercell with a 
regular distribution.

 > I have a very basic question concerning the 
supercell setup.
> My material is #166(R-3m) with O at (0,0,0.26), Mn at (0,0,0) and Li at
> (0,0,0.5). [These are hexagonal coordinate, and they are easily converted
> to (0.26,0.26,0.26), (0,0,0) and (0.5,0.5,0.5) in rhombohedral system.]
> I want to replace half Mn with Ni. So seems I need to build a supercell.
> I created the case.struct by StructGen. Then run "supercell" from the
> command line. Only specified the dimensions to double along x,y,z and kept
> other default setting. The program wouldn't run, here is the displayed
> message:
> >>>>
>  Program generates supercell from a WIEN struct file.
> 
>  Filename of struct file:
> 
>  Fatal Error occured:
>  Unknown lattice type: R
> 
>  Program terminated.
> 
> 0.001u 0.000s 0:00.00 0.0%	0+0k 0+0io 61pf+0w
> >>>>
> I thought this was because all atoms were on their ideal positions as told
> in the FAQ. I tried to modify the structure from StructGen. Putting lables
> on Li/Mn, it doesn't work (it should not work since only one position
> for Li/Mn in the cell). Displacing one of the O position slightly, this
> changed the O multiplicity from 2 to 6. But when run supercell to double
> the size, above message appeared again.
> I know there must be something wrong in my method to break the symmetry.
> But I don't know where this mistake was.
> So the question become quite basic--how to make some atomes different in
> the case. struct file or in StructGen? I worried that the multiplicity
> will also work on the modifications so that more positions thant I expect
> will be changed, even if I can make some change on the file. Who can give
> me advice to have the "supercell" run?
> 
> Thanks a lot
> 
> 
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> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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