[Wien] Electric Field Effects

[Peter Blaha]

It depends a bit on what you are looking for.
We were interested in GaAs and the relative change of positions of Ga and As atoms
under the E-filed.
For this question such large cells are necessary, because in this setup we had 2 kinks
and the relaxations near the kink are very much influenced by them.

In fact, nowadays I would do it differently, namely exactly as you have in mind:

In a slab geometry (surface) one can make this kink in the vacuum region and we have now
even asymmetric fields, so that you can put the strong variation into the vacuum.

In any case, as far as I remember it was a tedious work.

Better approaches are now done using a "Berry"-phase method and as far as I know, Oleg Rubel
(rubelo at tbh.net) has such an approach programmed into WIEN2k.

Am 06.08.2012 16:38, schrieb Paul Fons:
> Hi All,
> 	I have been studying the work of Stahn, Pietsch, Blaha, and Schwartz on electric field induced charge density variations (in GaAs) [PRB v63, 165205 (2001).  I had a couple of quick questions.  In the paper a large (22 formula units) of GaAs is used and the field is inverted halfway across the cell in the z-direction (e.g. to maintain the periodic boundary conditions).  I am curious to know if such a large number of repeats is necessary or is it simply necessary to have the field applied over a minimum spatial length.  First, what is the case for GaAs, can the number of repeats be varied without large changes in the result?  The second question has more to do with the sort of systems I wish to calculate E-field-induced effects upon.  They are already quite large in size with about 20 layers in a supercell and I would like to avoid making the cell unnecessarily large.  Would it make sense to make a vacuum layer between two units cells (and leave the electrostatic inflection!
  po
>   int there).  I assume I would have to fix the positions of the atoms at the end of the cell next to the vacuum layer if I did this.  Does this make sense?  Any advice on what cell sizes would be appropriate would be gratefully received.
>
> 				Paul Fons
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                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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