[Wien] Supercell and point simmetry

[Peter Blaha]

Once you have created the supercell, you have to "break" the symmetry.
This can be done in two ways:

a) Introducing a small shift in some coordinates. This, however, will
reduce the spacegroup to some lower one (maybe even to P1)
b) Introduce an impurity,vacancy,.... i.e. either replace one of the atoms
by an impurity or remove it. Alternatively, you can also simply "label"
ONE (only one at the beginning!!)  atom, eg. Cd1   instead of just   Cd
Then WIEN "knows" that this atom should be "different" from the others,
but still will maintain the highest posible symmetry.
Note, however, that this procedure is potentially dangerous, because you
restrict the relaxations around this impurity to a highly symmetric one.
Anyway, if this is what you want then this is the most efficient way.


> I'm using wien in the calculation of relaxed structures around dopants in
> diamond/zincblende structures. In some papers [ex. S. Lany et al. PRB 62
> (2000) R2259] i've found that, in order to reduce computational time a Td
> point group simmetry around the dopant is mantained in the supercell (SC).
> How is this realized in practice ?
>
> Normally I define a 16 atoms SC with all independent atoms (by applying
> small perturbations to the coordinates in order to remove equivalency) but
> doing this to a 32 or 64 SC should lead to unacceptable minimization times
> (in my case 4-5 days for a 16 atom SC).
>
> Is there a smart way to modify the original output of the program supercell
> to obtain a new one that preserves the Td point symmetry ?
> ****************************************************************************
> dr. Francesco d'Acapito
> GILDA CRG c/o ESRF
> BP220 F-38043 Grenoble (F)
>
> Tel +33 4 76882426   Fax +33 4 76882743
>
> e-mail: dacapito at esrf.fr
> URL: http://www.esrf.fr/exp_facilities/BM8/handbook/control.html
> ****************************************************************************
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>


                                      P.Blaha
--------------------------------------------------------------------------
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/
--------------------------------------------------------------------------