Extracting the value of electron phonon coupling strength for a paricular phonon band for a particular q point.

[Bikash]

Dear all,

Is it possible to get information about the electron-phonon coupling strength
for a particular phonon band for a set of selected q points?

Please let me know how if this is possible.

With regards,
Bikash Patra
TIFR, Mumbai

[gkafle1]

Hi Bikash,

Yes, it is possible to do that. If you set "phonselfen=.true." in your epw input, you will get lambda.phself file. This file contains information about the electron-phonon coupling strength for different modes along a q path that you specify.

Thanks!

Gyanu

[Bikash]

Dear Gyanu,

Thank you for your answer.

If I run "phononselfen=.true.", I get a lambda.phself file at 300 K.
Is the electron-phonon coupling constant depend on temperature?
The reason I am asking is that in the superconducting calculation, we use the same
electron-phonon matrix element at different temperatures.

with regards,
Bikash

[gkafle1]

Hi Bikash,

When you set "phonselfen=.true." in your EPW, you get lambda.phself file calculated from "selfen_phon_q" subroutine. This subroutine first calculates the imaginary part of the phonon self-energy (which is linewidth) and the e-ph coupling is calculated using the linewidth as shown by the attached equation (e-ph-coupling.jpg). In this equation, lambda_qv is calculated using the Fermi occupation factors, f_nk and f_mk+q, which depend on temperature. In the case of superconductivity calculation, you get lambda_qv using a double delta approximation (e-ph-coupling-2.jpg) as calculated in "evaluate_a2f_lambda" subroutine which was obtained by simplifying the Fermi occupation factors (in e-ph-coupling.jpg) using Taylor expansion. Based on my test, both subroutines give identical e-ph coupling.

Thanks!

Best
Gyanu