Dear all,
Is it possible to get information about the electronphonon 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
Extracting the value of electron phonon coupling strength for a paricular phonon band for a particular q point.
Moderator: stiwari
Re: Extracting the value of electron phonon coupling strength for a paricular phonon band for a particular q point.
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 electronphonon coupling strength for different modes along a q path that you specify.
Thanks!
Gyanu
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 electronphonon coupling strength for different modes along a q path that you specify.
Thanks!
Gyanu
Re: Extracting the value of electron phonon coupling strength for a paricular phonon band for a particular q point.
Dear Gyanu,
Thank you for your answer.
If I run "phononselfen=.true.", I get a lambda.phself file at 300 K.
Is the electronphonon coupling constant depend on temperature?
The reason I am asking is that in the superconducting calculation, we use the same
electronphonon matrix element at different temperatures.
with regards,
Bikash
Thank you for your answer.
If I run "phononselfen=.true.", I get a lambda.phself file at 300 K.
Is the electronphonon coupling constant depend on temperature?
The reason I am asking is that in the superconducting calculation, we use the same
electronphonon matrix element at different temperatures.
with regards,
Bikash
Re: Extracting the value of electron phonon coupling strength for a paricular phonon band for a particular q point.
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 selfenergy (which is linewidth) and the eph coupling is calculated using the linewidth as shown by the attached equation (ephcoupling.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 (ephcoupling2.jpg) as calculated in "evaluate_a2f_lambda" subroutine which was obtained by simplifying the Fermi occupation factors (in ephcoupling.jpg) using Taylor expansion. Based on my test, both subroutines give identical eph coupling.
Thanks!
Best
Gyanu
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 selfenergy (which is linewidth) and the eph coupling is calculated using the linewidth as shown by the attached equation (ephcoupling.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 (ephcoupling2.jpg) as calculated in "evaluate_a2f_lambda" subroutine which was obtained by simplifying the Fermi occupation factors (in ephcoupling.jpg) using Taylor expansion. Based on my test, both subroutines give identical eph coupling.
Thanks!
Best
Gyanu
 Attachments

 ephcoupling2.jpg (8.89 KiB) Viewed 22641 times

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