EPW Forum

Dear experts,

I am trying to calculate momentum dependent electron-phonon coupling (EPC) using EPW code, and I came across with the website of EPW documentation https://docs.epw-code.org/doc/Electron-phononCoupling.html, where EPC it is shown how gkk is calculated using dV_scf. Now from the DFT phonon calculation we can calculate dV_scf which is stored in some *dvscf files, which we can't access directly.

I am interested in calculating gkk from dvscf, is there any way I can access those files, and then also is there any relevant paper where it is discussed how to calculate gkk from dvscf?

Can we also calculate a derivative of gkk w. r. to u_q. Can this be calculated straight-forwardly from the derivative of dV_scf? In any case, I will need to access dV_scf.

I would appreciate any relevant paper, where I can read about the theory to calculate gkk from dV_scf, and also the source code file where gkk is actually calculated.

Thank you,
Shubham

Dear Subham,

The dvscf files are available in the _ph0 folder, but they are in binary format.

You can calculate gkk from DFPT calculations using the following tags: You can find the tutorial in the following link
https://epw2024.oden.utexas.edu/74-schedule for Tue 2.30 seesion material.

If you are referring to calculating the Debye–Waller term for the derivative of gkk with respect u_q, you can do so using WFPT. Please see the Friday 3:15 PM tutorial with the previous link by Jae-Mo Lihm(https://drive.google.com/file/d/1ag7lxFEwyibJysq5Tp9d9acQgo9mDTys/view).

Please let me know if you need further help.

Regards,
Shashi

Dear Shashi,

Thank you so much for the tutorials. I also found Lihm's slides there, which are really helpful.
Moreover, I wanted to know that if the data stored in the dvscf files is in the momentum space (q) or the real space(r)? After, doing some search I found it is stored in the q space, and using some utility I can convert it into the r-space which is now stored in some other binary files called 'prefix.w_pot.irc*.dat'. So, my question is that could you please tell me how can I extract the data stored in those binary files to some human-readable data? Or could you tell, what is the structure of data. I could extract some data but don't understand the grid structure. I would be really grateful if you could help me with this technicality.

Thanks again.

Regards,
Shubham