BSE calculations in spin-polarization systems

Deals with issues related to computation of optical spectra, solving the Bethe-Salpeter equation.

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Jing Liu
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BSE calculations in spin-polarization systems

Post by Jing Liu » Tue Mar 01, 2022 1:25 pm

Dear all,
Considering the spin-polarization system, I have a question that how to obtain the imaginary part of the BSE dielectric function with contributions from individual spins in practice
BSE for individual spins.png? (example shows in the attachment) https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.236402 [attachment=0]BSE for individual spins.png
I have done an attempt in a FM semiconductor but I am not sure whether I am right. :idea:
For the spin-up channel, the filled bands are 1-64, while the empty bands are 65-240. For the spin-down channel, the filled bands are 1-60. Therefore, when I want to obtain the absorption spectrum of the spin-up channel, I set the tag "% BSEBands" as 63 | 68 in which two valence bands and four conduction bands are considered to build the BSE Hamiltonian. In this way, no transitions from the spin-down channel are included, right?
In the same way, if I set the "% BSEBands" as 59 | 64, only the transitions from spin-down channel are considered, right?
Thanks so much for any kind suggestions~ ;)

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: BSE calculations in spin-polarization systems

Post by Daniele Varsano » Wed Mar 02, 2022 8:45 am

Dear Jing,

given your electronic configuration with the setting you are using you are indeed looking at transition coming from a selected spin channel. The problem I see anyway is that it is not guaranteed that the spectra are converged.

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: BSE calculations in spin-polarization systems

Post by Jing Liu » Wed Mar 02, 2022 8:55 am

Dear Daniele,
Thanks for your reply.
But in which way I can use to obtain the BSE from individual spins correctly?

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

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Davide Sangalli
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Re: BSE calculations in spin-polarization systems

Post by Davide Sangalli » Thu Mar 03, 2022 12:10 pm

This feature is not coded.
But you can open the file src/bse/K_Transitions_setup.F and change the loop

Code: Select all

do i_sp_c=1,n_sp_pol
to

Code: Select all

do i_sp_c=1,1 !(for spin up)
and to

Code: Select all

do i_sp_c=2,2 !(for spin down)
So you would have two different executables.

Best,
D.
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
https://sites.google.com/view/davidesangalli
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Jing Liu
Posts: 21
Joined: Wed May 06, 2020 8:48 am

Re: BSE calculations in spin-polarization systems

Post by Jing Liu » Thu Mar 03, 2022 12:58 pm

Dear Davide,
Thank you so much~ I'll try!

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

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Davide Sangalli
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Re: BSE calculations in spin-polarization systems

Post by Davide Sangalli » Tue Jul 12, 2022 12:53 pm

Just a warning.
The BSE mixes spin-up and spin-down transition.
With the change I suggested you avoid such mixing.
So the resulting spectrum will not be just the full one projected on the spin channel, but it could be substantially different.
Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre
https://sites.google.com/view/davidesangalli
http://www.max-centre.eu/

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