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electron-phonon matrix elements 
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Joined: Tue Nov 20, 2018 10:43 am
Posts: 3
University: Uppsala University
Post electron-phonon matrix elements
Dear All,

I am a participant of 'School on Electron-Phonon Physics from First Principles' held at the International Centre for Theoretical Physics in Trieste on 19-23 March 2018. It was a very good school and I had a great experience attending the School.

On Tuesdays Hands-on section, we tried to compute the electron-phonon matrix elements using a slightly modified phonon program (which includes printing information). It seems like the output from those calculations are '|g(q-point, frequency, band1, band2)|'. The g-matrix should be a function of k-point also, which is missing in the output. I found on the subroutine 'elphel' it is mentioned that

-------------------
write(6,*)
write(6,*) 'We here write only the matrix elements for k=Gamma in the first proc:'
write(6,*)
!
! consider only initial state k=0
-------------------

Does this mean that all the |g| written on the output file are for k=0? In this case how one can get |g| as s function of k-point as well.

Thank you for your time and consideration,
Best regards,
Fairoja.
-----------
Fairoja Cheenicode Kabeer
Postdoctoral researcher,
Materials Theory,
Uppsala University.


Wed Nov 21, 2018 8:56 am
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Joined: Wed Jan 13, 2016 7:25 pm
Posts: 532
University: Oxford
Post Re: electron-phonon matrix elements
Dear Fairoja,

You can consider any state. We only show the el-ph matrix element at k=\Gamma and then changed q.
However you can look at any k-point.

In the code you have:
Code:
  ! consider only initial state k=0
  ik = 1
  WRITE(6,'(a,3f10.6)') 'xk ', (xk(n,ik),n=1,3)


where ik=1 is in this case the Gamma point. You can just change that value to get different k-points.
Note that you can also add k-point loop around all of that like this
Code:
DO ik=1, MAX_NUMBER_OF_K_POINTS
  WRITE(6,'(a,3f10.6)') 'xk ', (xk(n,ik),n=1,3)
  write(6,*) ' ibnd  jbnd  imode   eig_i (eV)    eig_j (eV)   omega_nu (meV)    |g| (meV)'
...
ENDDO


Be careful that this will generate very large txt files (lots of data).

Best wishes,
Samuel

_________________
Dr. Samuel Poncé
Department of Materials
University of Oxford
Parks Road
Oxford OX1 3PH, UK


Thu Nov 22, 2018 10:25 am
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