[Wien] Impurity sites in supercell

[Shu Miao]

Dear Stefaan
I think this is a general issue related to multiplicity. Assuming atom
A has N multiplicity with coordinate (x,y,z) in the original cell, there
will be L A atoms in the LxLxL supercell and each has N multiplicity with
coordinates (x+n1*a,y+n2*b,z+n3*c), where a,b and c are the original
lattice parameters and n1,n2 and n3 are integers less than L. In the
StructGen template, only the first one among the N positions can be edited
and all others are changed automatically be symmetry operations. So a
localized defect cluster is created in stead of a single defect. This will
happen as long as atom A has a multiplicity greater than 1.
What I am doing now is first to build a P type cell and put a label on
every position so that multiplicity is 1. Then make change on the position
as I want. Finally, remove all the labels on other positions and run
init_lapw to let Wien2k to find out the remaining symmetry. My case
contains 28 positions, it is a kind of pain to build the cell. For more
complex cases, this way is not very practical.


Shu Miao

On Tue, 19 Sep 2006, Stefaan Cottenier wrote:

>
> Check what you gave as target type. If you use B as target, then the
> impurity will be put at 0 0 0 and 1/2 1/2 1/2, if you put P then it will
> be only at 0 0 0. Perhaps this causes your problem?
>
> Stefaan
>
> >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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> >
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