[Wien] exciton trapping

Laurence Marks L-marks at northwestern.edu
Thu Mar 1 12:15:51 CET 2012

At least with Wien2k you cannot tell the electrons where to go.

Have you looked at the optic code results?

Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu 1-847-491-3996
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
 On Mar 1, 2012 2:47 AM, "Fabiana Da Pieve" <fabiana.dapieve at gmail.com>

> Hello wien2k users
> I am maybe going to ask a trivial or a totally non-sense question, but I
> am trying to do what I can with what I have.
> I know that at the moment BSE calculations with wien2k (and other codes)
> are very computationally demanding, and in any case the BSE part is still
> not released.
> In any case, even if it would be released, I think I could not run it on
> my system because it is very heavy.
> However, I would like to find a way (even a very simple one) to see if a
> certain optical excitation would lead to a localized exciton (which
> localizes because of local distortion for example) or if such optical
> excitation would not lead to any distortion. I would like to study this
> because sometimes excitonic transitions could change bond lengths and
> change (slightly, I think) the covalency of a certain bond, and in such
> distortion the exciton could be trapped, which is want I want to see.
> So, I was thinking that MAYBE I could have "a first idea" of the eventual
> distortion induce by my optical ideal exciton already at the DFT level in
> the following way:
> 1) I remove an electron from one of the external levels of the anion in
> which I believe the hole is created in the file......(ok, very bad thing,
> optical excitations cannot be described as localized on a single site at
> the beginning)
> 2) at this point, either I smear the charge uniformly in space  (or maybe
> I could explicitly put an electron more in the orbital of the cation which
> I know is the acceptor orbital ??)
> 3) instead of running a normal scf calculation, I run a structural
> optimization calculation (keeping the lattice parameters fixed, i.e. moving
> only atoms)
> 4) at the end I analyze the changes in the bond lengths near the atom
> Is it correct (at least as a very zero approximation to the problem) ?
> totally wrong ?
> Any suggestions is welcome !
> Thanks !
> Fabiana
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