full BSE calculation

Run-time issues concerning Yambo that are not covered in the above forums.

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Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: full BSE calculation

Post by Jing Liu » Fri Nov 05, 2021 11:20 am

Dear Daniele,
I have checked my "o-BSE.exc_E_sorted" file and find the positive and negative value are almost symmetrical. In my corresponding TDA calculation, the lowest exciton energy is negative and shows the excitonic instability.
Could you please tell me how can I (or in which output file) find "the negative eigenvalues having v-->c components in their eigenvectors" in full BSE calculation?

Thanks so much!
Best,
Jing
Jing Liu
PhD student
Beijing Institute of Technology, China

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Daniele Varsano
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Re: full BSE calculation

Post by Daniele Varsano » Fri Nov 05, 2021 12:06 pm

Dear Jing,
in TDA only v-->c transitions are taken into account.
In order to inspect the transitions forming the exciton you need to print the weights !Acv!^2 as explained in the tutorials e.g:

http://www.yambo-code.org/wiki/index.ph ... 021_school

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/

Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: full BSE calculation

Post by Jing Liu » Fri Nov 05, 2021 1:02 pm

Dear Daniele,
Thanks for your kind reply!

Best,
Jing
Jing Liu
PhD student
Beijing Institute of Technology, China

Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: full BSE calculation

Post by Jing Liu » Thu Nov 11, 2021 12:40 pm

Dear Daniele,
I have calculated the weight of different exciton states after the full BSE calculation.

1. In order to look at exciton instabilities, I chose some of the negative excitations to check whether there are v-->c components in their eigenvectors.
I have uploaded the "o-BSE.exc_E_sorted" file and also the "o-BSE.exc_weights_at_110" file.
I found there are v-->c components in this negative excitations. Does it means that there exists exciton instability in this system? The corresponding energy is "-0.2704 eV". Does it means that the lowest exciton transition energy is "-0.27 eV"? (My TDA calculation shows the lowest exciton energy is -0.27 eV).
But however, I also did a test of the weight of state "175" (the corresponding energy is -1.019 eV), there are also v-->c components.
So I am confused that how to verify the lowest exciton transition energy?

2. I also did a full BSE test in a semiconductor system (not an intrinsic excitonic insulator predicted by TDA). But I found the weight of several negative excitations also have the v-->c components, does it means that there are also exciton instabilities in this system? Not as predicted as TDA?

Thanks so much!

Best,
Jing
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Jing Liu
PhD student
Beijing Institute of Technology, China

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Daniele Varsano
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Re: full BSE calculation

Post by Daniele Varsano » Thu Nov 11, 2021 1:44 pm

Dear Jing,

if the coupling has an effect of course v->c and c->v do mix (by definition!) so you will have always a small component from both transition.
My warm suggestion is to stay in TDA approximation (as you also verified that coupling does not have great effect) where the picture is more clear for interpretations.

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/

Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: full BSE calculation

Post by Jing Liu » Thu Nov 11, 2021 1:56 pm

Dear Daniele,
If the "coupling" has a great effect, how to judge the excitonic instability?
It seems that the "weight" can not give a specific criterion.

Thank you!

Best,
Jing
Jing Liu
PhD student
Beijing Institute of Technology, China

User avatar
Daniele Varsano
Posts: 3773
Joined: Tue Mar 17, 2009 2:23 pm
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Re: full BSE calculation

Post by Daniele Varsano » Thu Nov 11, 2021 2:09 pm

Dear Jing,
if the system is unstable wrt e-h formation it will appear as negative eigenvalue in the TDA.
Coupling can be seen as a perturbation to the resonant and anti-resonant part.

If unstable you will have negative eiegenvlues with mainly v->c components (resonant) and positive eigenvalues with mainly c-->v (antresonant) component.

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/

Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: full BSE calculation

Post by Jing Liu » Fri Nov 12, 2021 1:53 am

Dear Daniele,
Thanks so much!

Best,
Jing
Jing Liu
PhD student
Beijing Institute of Technology, China

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