Overestimated binding energy

Deals with issues related to computation of optical spectra in reciprocal space: RPA, TDDFT, local field effects.

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Nhat Minh Pham
Posts: 14
Joined: Tue Feb 15, 2022 12:07 am
Location: 01 Mac Dinh Chi, Ben Nghe, District 1, Ho Chi Minh City, Viet Nam

Overestimated binding energy

Post by Nhat Minh Pham » Wed Nov 23, 2022 3:53 am

Dear users and developers,
I'm using Yambo to get monolayer MoS2 optical absorption spectrum from solving BSE.
But the result has a large redshift with over 1 eV of binding energy, which causes the first peak to locate at 1.5 eV.
I used Yambo 5.1 to get a gap of about 2.55 eV and calculated BSE from that with 15x15 grid (non-SO) and
45x45 grid (with SO). They both show the first peak at 1.5 eV, far from PhysRevB.88.045412 result.
Please help me fix it. My BSE input and spectrum are attached below.
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Pham Nhat Minh
MS student, Ho Chi Minh University of Science,
Ho Chi Minh City Institute of Physics
https://www.hcmus.edu.vn/

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Daniele Varsano
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Re: Overestimated binding energy

Post by Daniele Varsano » Wed Nov 23, 2022 8:32 am

Dear Pham Nhat Minh,

one inconsistency I can see in your input is that you ask for 20Ry in BSENGBlk, but only 8Ry are considered in NGsBlkXs.
Check if this is a source of error. Next, it would be useful to look at the report file in order to see if there are other problems.

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/

Nhat Minh Pham
Posts: 14
Joined: Tue Feb 15, 2022 12:07 am
Location: 01 Mac Dinh Chi, Ben Nghe, District 1, Ho Chi Minh City, Viet Nam

Re: Overestimated binding energy

Post by Nhat Minh Pham » Thu Nov 24, 2022 10:55 am

Thank you, Daniele

My calculation for 45x45 grid was bad, and the fast convergence of binding energy from references made me panic.
BSE is slow to converge with Kpoint-sample. Is there any good way to make it fast as Yambo 5.1 does with GW?

Best,
Minh
Pham Nhat Minh
MS student, Ho Chi Minh University of Science,
Ho Chi Minh City Institute of Physics
https://www.hcmus.edu.vn/

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Daniele Varsano
Posts: 3880
Joined: Tue Mar 17, 2009 2:23 pm
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Re: Overestimated binding energy

Post by Daniele Varsano » Wed Dec 07, 2022 10:49 am

Dear Minh,

the Wrim technique in principle can be also used for BSE, but I would not suggest using it. Even if it can speed up the calculation, it can also brings you to non accuarte results depending on the nature (localized or delocalized) of the exciton.

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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