[Wien] Impurity sites in supercell

[Torsten Andersen]

Dear Shu Miao,

this is probably not what you want. I would expect that you want them to 
be inequivalent because of the IA. Therefore, you should give each 
position an inequivalent atom, i.e., OA1 OA2 OA3 OA4 and repeat the atom 
specification clauses for each atom. Finally, remove all symmetries and 
run it through init_lapw.

You will, of course, get a periodic arrangement of IA's (one in each 
unit cell) in the bulk, but that is a feature of bulk codes...

Best regards,
Torsten Andersen.

Shu Miao wrote:
> Dear Wien users
> I have a question in building a supercell. As said in the UG, one should
> make some change on an atom in the expended cell, e.g. 2x2x2, to build a
> supercell compatible with symmetry operations. Assuming 4 atoms in the
> original cell, then we have 32 atoms in the expanded cell. If I replace
> atom OA with an impurity IA, the final structure will be 31 original
> atoms plus IA. However, IA has equivalent positions at (x/2, y/2,
> z/2), where (x,y,z) are the equivalent positions of OA in the original
> cell. These sites of IA are within a 1/8 corner of the expanded cell. So
> what we create actually is a localized cluster of IAs. Is this what the
> supercell program surposed to do, or I do something wrong? Is there a way
> to create even distribution of the impurity in the expanded cell or just
> one impurity site in the super cell? Many people talking about the
> applicaiton of the supercell in the mailing list, but I didn't find
> concerns about the distribution of impurities within the supercell.
> Why? Because this won't make difference?
> Please advise.
> Many thanks
> 
> Shu Miao
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-- 
Dr. Torsten Andersen        TA-web: http://deep.at/myspace/
AG Hübner, Department of Physics, Kaiserslautern University
http://cmt.physik.uni-kl.de    http://www.physik.uni-kl.de/