Perform electron-Phonon coupling

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Affiliation: University of Dschang

Perform electron-Phonon coupling

Post by Lavoisier »

I performed a Hands-on tutorial of "Ponce" on electron-phonon matrix elements. And I have a couple of questions please. I am a new user

1- I obtained the interpolated band structure with EPW (BS_pw_epw.png) but still I don't understand what is different about it compared to the one obtained with pw.x. Maybe it should be the last band up and down? I thought after doing epw.x calculation, I will clearly see the influence of the electron-phonon (e-ph) coupling on the band structure of lead.

2-I noticed that the phonon frequencies (disp_pw_epw.png) calculated with both pw.x and epw.x perfectly coincide and I don't understand why?

3-After where I am to find the phonon linewidths, the imaginary part of the phonon self-energy and the electron-phonon strength associated to phonon modes and wave vectors, it is said that the phonon-self energy are respectively saved in the files linewidth.phself.XXXK and lambda.phself.XXXK. But, when I open the first file (linewidth.phself.0.075K) I only see the Phonon frequency and phonon linewidth. In the second file ( lambda.phself.0.075K) it is written "Lambda phonon self-energy". I am a bit confused because in the first file, I was to find the imaginary part of the e-ph self-energy and in the second file the e-ph coupling strength. So please, how should I exactly identify each of the three elements?

4-I was expecting that after taking into consideration the e-ph coupling and performing the epw.x calculation, I will observe a change in the band structure (like a change in the band gap for example) but I am really unable to point out the effect of the e-ph coupling after these calculations.

I'm looking forward to hearing from you.
Phonon frequency with pw.x and epw.x
Phonon frequency with pw.x and epw.x
disp_pw_epw.png (39.13 KiB) Viewed 16163 times
Band structure with pw.x and epw.x
Band structure with pw.x and epw.x
BS_pw_epw.png (48.28 KiB) Viewed 16163 times

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Joined: Tue Mar 21, 2017 7:11 pm

Re: Perform electron-Phonon coupling

Post by hpaudya1 »

Hi Lavoisier,

1 and 2. The interpolated band/phonon looks good. In the band structure, the top and bottom bands with PW are not included in the wannierization, so you do not see in the EPW calculation.

3. I think, you need to read EPW documentation in more details.

4. No, EPW does not help improve the band gap and etc.

Happy EPWing,

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