finite temperature absorption spectrum for hBN

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ymzhang
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Joined: Wed Jun 10, 2020 8:20 am

finite temperature absorption spectrum for hBN

Post by ymzhang » Sun May 29, 2022 4:57 pm

When I'm calculating h-BN absorption spectrum at room temperature. I find that I can't consider el-ph coupling and el-hole coupling at the same time.
I notice that there is a commented parameter:

Code: Select all

#WehCpl                        # [BSK] eh interaction included also in coupling
and I think that if I uncomment this parameter I can calculate the electron-hole attraction and electron-phonon coupling at the same time. But depending the
result in the attachment (the png file), I find that the first absorption peak for G0W0+BSE calculation (black line) appears at 3.6 eV or so. But the first 0K absorption peak
(red line) appears at 5.6 eV or so. I've include the G0W0 correction in terms of a 2.0 eV scissor operator. If the el-hole coupling is correctly included, the 0K absorption should have similar peak energy as the G0W0+BSE result since the epc correction is just perturbative and can't contribute such big discrepancy. Is the el-hole coupling really well-behaved in coupling mode BSE calculation?
Thanks
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Daniele Varsano
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Re: finite temperature absorption spectrum for hBN

Post by Daniele Varsano » Mon May 30, 2022 7:17 am

Dear ymzhang,

please sign your post with your name and affiliation, this is a rule of the forum and you can add once for all your signature in your user profile.

Here you can find a tutorial on finite temperature BSE:
http://www.yambo-code.org/wiki/index.ph ... emperature

Please note that WehCpl is meant to add the direct part of the kernel in the coupling part, usually, this is negligible and that's why it is not included by default.

In one of your inputs "yambo_0K_BSE.in" it seeme the QP correction has been taken into account twice (read from a QP database and using a scissor operator on top).

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/

ymzhang
Posts: 5
Joined: Wed Jun 10, 2020 8:20 am

Re: finite temperature absorption spectrum for hBN

Post by ymzhang » Tue May 31, 2022 2:24 pm

Thanks for your reply.
I include the correction twice because the electron-phonon coupling and G0W0 correction are added separately. The epc db is include in T0/ndb.QP while the G0W0 correction is given by a 2.0 eV scissor. In view of my G0W0+BSE absorption, the electron-hole attraction is important and will introduce a 2 eV discrepancy between the first absorption peak and the G0W0 bandgap. But in the EPC+BSE absorption the 2 eV energy difference is missing. So I think the electron-hole attraction is not successfully included.

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Daniele Varsano
Posts: 3773
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Re: finite temperature absorption spectrum for hBN

Post by Daniele Varsano » Mon Jun 06, 2022 5:09 pm

Dear ymzhang,
as already written in the first answer:
please sign your post with your name and affiliation, this is a rule of the forum and you can add once for all your signature in your user profile.

IN order to check if you are including the QP corrections correctly you an inspect and compare the independent-particle spectra, they are reported in the 4th column of the output.

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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