Yambo Community Forum

Posted: **Thu Sep 15, 2022 5:29 am**

Dear all,
I use the yambo 4.5.3 (sorry for no upgrade because I have no authority in our cluster). As an example, I run a spin polarization calculation on two-dimensional CN system using the PW program. As shown in PW output (see attached file yb_pwscf.out), the system has 9 electrons with 5 up and 4 down. Then I run the BSE calculation and modify the code of ypp (excitons_driver.F) to print out the BSS_eh_table (see attached file YBBSEEHT.txt).

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do I = 1, BSS_n_eig
     if(n_sp_pol==1) write(200,'(1X,3I4,"  1 ")')  BSS_eh_table(I,:)
     if(n_sp_pol==2) write(200,'(1X,4I4)')  BSS_eh_table(I,:)
enddo

As showed in YBBSEEHT.txt, for k1 point, the valance(v)-conduction(c) transition pairs are constructed by

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  k   v   c   spin
  1   4   5   1
  1   4   5   2
  1   4   6   1
  1   4   6   2
  1   4   7   1
  1   4   7   2

In the BSE calculation, the following was set (see attached file bse.in)

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% BSEBands
  4 | 7 |                     # [BSK] Bands range

My question is why the 4->5 transition pair is constructed for both spins.
Could you give me some hints or references for constructing the BSE matrix in the spin polarization calculation?

Best regards.
Youzhao Lan

Posted: **Thu Sep 15, 2022 7:17 am**

Dear Youzhao,

this happens because band "5" is seen by Yambo as metallic:

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 [X]States summary         : Full        Metallic    Empty
  [X]             [spin up]      0001-0004   0005-0005   0006-0010
  [X]                  [dn]      0001-0004   0005-0005   0006-0010

and this is due to previous QE calculation:
Please check also your QE output!

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highest occupied, lowest unoccupied level (ev):     0.3223   -1.9154

where you have the lowest unoccupied states lower than the highest occupied states. You can try to do a setup setting ElecTemp=0 eV, but I'm not sure that this will solve the problem. Check first the QE ground satate.
My suggestion is to use a smearing in the occupation.
Finally, my strong suggestion is to move to a more recent version of the code (ask your administrator) as the code has changed and improved a lot since the version you are using, in particular in the handling of spin polarized calculation.

Best,
Daniele

Posted: **Thu Sep 15, 2022 7:27 am**

Dear Dr. Daniele,
Thanks for your quick help.
Best,
Youzhao Lan

Yambo Community Forum

How to construct the BSE matrix for spin polarization calculation in Yambo

How to construct the BSE matrix for spin polarization calculation in Yambo

Re: How to construct the BSE matrix for spin polarization calculation in Yambo

Re: How to construct the BSE matrix for spin polarization calculation in Yambo