Hello everyone:
I have a question to ask you, that is, how should I set the fsthick parameter when I calculate the electro-acoustic coupling and superconducting gap? Is it related to

k + q = k'

? I can't find any analytical material about them.Have clear this knowledge elder broad to help answer it? thank you!

You need to do convergence tests for few values of fsthick. You can start from 4 times the maximum phonon frequency of your system (many times I have found we do not need to go beyond). For example, in MgB2, the maximum phonon frequency is around 100 meV, so we have used fsthick = 0.4 eV, which is 4 times the maximum phonon frequency (see: https://gitlab.com/QEF/q-e/-/blob/devel ... epw.in#L33).
I hope it helps.

PS) Could you please sign your name and your affiliation in your future posts.

Dear Hari ,
Ok, thank you. The solution is very helpful to me. But is there any advice to explain the problem from a theoretical perspective?
Sincerely,
dhwu