optical transition analysis

Deals with issues related to computation of optical spectra, in RPA (-o c) or by solving the Bethe-Salpeter equation (-o b). Includes local field effects, excitons, etc.

Moderators: Davide Sangalli, Daniele Varsano, andrea.ferretti, andrea marini, Conor Hogan, myrta gruning

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Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

optical transition analysis

Post by Weiqing Zhou » Mon Jul 22, 2019 1:17 pm

Hi all,

If I want to know that a peak contributed by which transitions, can yambo give corresponding information ?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072

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Daniele Varsano
Posts: 2655
Joined: Tue Mar 17, 2009 2:23 pm
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Re: optical transition analysis

Post by Daniele Varsano » Mon Jul 22, 2019 1:24 pm

Dear Weiqing,
this can be done by using the ypp utility.

Code: Select all

ypp -e a 
to generate the input to choose the exciton you want to analyse, and then run ypp.
The BSE need to be solved by uncommenting the WRbsWF variable.
In order to select the excitation run ypp -e s first you will have the excitation energies and corresponding index.

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

Re: optical transition analysis

Post by Weiqing Zhou » Mon Jul 22, 2019 1:31 pm

Dear Daniele,

Thanks!
But can I do this analysis for RPA optical absorption instead of BSE ?

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072

User avatar
Daniele Varsano
Posts: 2655
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: optical transition analysis

Post by Daniele Varsano » Mon Jul 22, 2019 1:32 pm

It can be done if the RPA is solved in transition space,

Code: Select all

yambo -o b -k hartree -y d
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

Weiqing Zhou
Posts: 48
Joined: Thu Sep 06, 2018 7:57 am
Location: Wuhan University

Re: optical transition analysis

Post by Weiqing Zhou » Tue Jul 23, 2019 9:06 am

Dear Daniele,

1. Why you say yambo -o b -k hartree -y d is a RPA one ? I think RPA optics should be yambo -o c.

when I use ypp -e a, I find input is :
--------------------------------------------------------------------------------
excitons # [R] Excitons
amplitude # [R] Amplitude
States= "1 - 1" # Index of the BS state(s)
#DipWeight # Weight the contribution to the exciton WFs with the dipoles
Degen_Step= 0.0100 eV # Maximum energy separation of two degenerate states
---------------------------------------------------------------------------------
2. What does 'States' mean ? the index of peak in absorption ? If I want to know the contribution of 2-nd peak, what should I set ?

3. the output files are o.exc_amplitude and o.exc_weights. What information do they contain ?

Actually, what I want to know is that a 1.3 eV peak is mainly contributed from what transitions.

Best,
Weiqing
Weiqing Zhou
Phd student
Wuhan University
Wuhan, Hubei, 430072

User avatar
Daniele Varsano
Posts: 2655
Joined: Tue Mar 17, 2009 2:23 pm
Contact:

Re: optical transition analysis

Post by Daniele Varsano » Tue Jul 23, 2019 9:50 am

Dear Weiqing,
1. Why you say yambo -o b -k hartree -y d is a RPA one ? I think RPA optics should be yambo -o c.
Both are RPA calculated on a different basis (transitions vs reciprocal lattice vector). If you want to analyze your peak you need to perform calculations in the transition space.
What does 'States' mean ? the index of peak in absorption ?
No, it is the index of the excitation sorted by energies, you can have dark excitation you cannot see by looking at the spectra.
As stated above you need to sort your excitation by running:

Code: Select all

ypp -e s 
you will have as output two files with the excitation ordered by energy and by intensity, there you can identify your peak and see the corresponding index. This is the index you need to set in the ypp input.
the output files are o.exc_amplitude and o.exc_weights. What information do they contain ?
As reported in the header of the o.exc_weights file you have the transition that mostly contributes to that excitation, so what you are looking for.

For a step by step guide you can have a look at this tutorial:
http://www.yambo-code.org/wiki/index.ph ... e_excitons

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

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