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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,*) 'We here write only the matrix elements for k=Gamma in the first proc:'
! 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 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:
  ! 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
  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)'

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

Best wishes,

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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