[Wien] absorption coefficient

[fatima DFT]

thank you very much Prof. Blaha and Pavel,

Prof. Blaha: Yes, in the paper author reported the sharp peal for lowest
exciton transition using BSE theory.

Prof. Pavel:

I do not have any experience about BSE calculations so for now I want to
bindup the project with DFT only.

I have finished the calculation with -SO now and the shape of the
absorption spectra has changes significantly.


The experimental band gap of the compound is 1.62 eV and I am getting it
1.1 eV with SO.
In the revised absorption coefficient calculated from Wien2k
<https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxkZnRmYXRpbWE1fGd4OjZiOGYyYTI3MGQ5N2RjMjk>,
the absorption peak starts from ~1.0 eV followed by a shoulder like shape
at ~3.eV.
In many literature paper, people reported a small broad peak around  1.7 eV
and then at ~2.5eV.

If I do a tau plot then the onsite absorption edge occurs at ~1.7eV.

My further queries are:

1. Should I report the tau plot to compare my tau plot peak with the the
sharp absorption peak observed in experiment
<https://4bd1924d-a-62cb3a1a-s-sites.googlegroups.com/site/dftfatima5/letter/mailing-list-queries/Absorption_coefficient.png?attachauth=ANoY7coNS62dJC53AmGkh7APGKhfUxz_3oOFRqExrGLyrEYsNFNkgZ8pobRnqjX3egrT7v3GI9sDrJAdvpcAao566zH-5Qk2Tw4q9vd3sYB9_tUu7lKV37w0JLbuje82aR3pXjpQ5iHJR595akXSNQXufL91mtvChfV0LJzB0z94VuI17_noK30lQPqiwXmTddqcQkupX-4_FHQtFJ0G6VadIfUExpWfFnVtyOsumMMrzAp6HrLT9YlrIpG7a_LkbFSSW8ff6fS31taZmDQW4VwtDIE5HlV9PA%3D%3D&attredirects=1>.
or
2. Is it possible to apply scissors correction so that my broad shoulder
like peak may shifts to lower energy side?

Thanks and regards
Ms. Fatima


On Fri, Aug 4, 2017 at 12:10 PM, Pavel Ondračka <pavel.ondracka at email.cz>
wrote:

> fatima DFT píše v Čt 03. 08. 2017 v 15:50 +0530:
> > Dear Users of Wien2k
> >
> > I want to simulate optical properties of a perovskite compound.
> > In the literature people have reported a sharp peak at 1.6 eV while I
> > am not getting it.
> > Here is the file from literature and here is the file that I got from
> > Wien2k.
> > Does including -SO in the calculation may effect the shape of the
> > absorption curve?
> >
> >
> > Regards
> > Fatima
> >
> Dear Fatima,
>
> it is hard to tell without the knowledge of the compound, however in
> general sharp peaks like this near the absorption edge are usually
> caused by excitonic effects, which are not included in the optic
> package (it uses just random phase approximation without local field
> effects). If you compound is not too complicated and you are skilled
> enough, you can try the BSE unsupported package which can calculate the
> optical spectra including the excitons to see it helps. Just be warned,
> it is unsupported and much less documented than the Wien2k standards.
> Moreover, to get even somewhat converged results requires a LOT of CPU
> time and a LOT of memory.
>
> Best regards
> Pavel
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