[Wien] How to use wien2k to calculate defect formation energy?

[Ricardo Faccio]

Hi
I agree what Steffan and Oleg said related to scaling a "defect free" cell 
in order to compare the total energy with a supercell with defects.
On the other hand, you have to take into account the fact that in a 
supercell (depending on the symmetry) you could have more degree of freedom 
due to the presence of inequivalent atoms. If you compare the total energy 
from a scaled defect free cell with a defect free supercell (with more 
inequivalent atoms than the original one) you will find small differences.
So you have to take into account the symmetry of your cells.
Regards
Ricardo
-------------------------------------------------------------------------
-----   Ing. Quím. Ricardo Faccio

Mail: Cryssmat-Lab., Cátedra de Física, DETEMA
Facultad de Química, Universidad de la República
     Av. Gral. Flores 2124, C.C. 1157
     C.P. 11800, Montevideo, Uruguay.
E-mail: rfaccio at fq.edu.uy
Phone: 598 2 9241860 Int. 109
           598 2 9290705
Fax:    598 2 9241906
Web:  http://cryssmat.fq.edu.uy/ricardo/ricardo.htm
----- Original Message ----- 
From: "Stefaan Cottenier" <Stefaan.Cottenier at fys.kuleuven.be>
To: "A Mailing list for WIEN2k users" <wien at zeus.theochem.tuwien.ac.at>
Sent: Wednesday, May 24, 2006 5:13 AM
Subject: Re: [Wien] How to use wien2k to calculate defect formation energy?


>
>>     In WIEN2k-FAQ, it said
>> it is usually NOT possible just to double the cells and leave all atoms 
>> at their ideal and equivalent positions. This would lead to large 
>> multiplicities (e.g. in big supercells even more than 48 atoms could be 
>> "equivalent" and of course there is NO SPACEGROUP corresponding to this 
>> type of cell, since they all can be reduced by translation symmetry.
>> But when we want to calculate the defect formation energy ,we need to 
>> calculate the nenergy of defect-free system.
>>So how to calculate the defect formation energy with wien2k?
>>
>>
> Calculate the energy for the defect-free single cell (not supercell),
> and multiply it by the ratio between the volumes of the supercell and
> the single cell. Just take care of your k-mesh, to have numbers of
> comparable accuracy: if the k-mesh for the supercell is b*b*b and that
> supercel is n*n*n times the single cell, then a comparable k-mesh for
> the single cell is nb*nb*nb.
>
> Stefaan
>
>
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