[QE-developers] interpolation scheme in the el-ph in PHonon code

[Mitsuaki Kawamura]

Dear Nadeem

Hello,
I highly recommend you to use the optimized tetrahedron method for the calculations of phonons and electron-phonon coupling constants.
I recommend also using denser k-grid for the calculation of electron-phonon coupling by specifying nk1, nk2, and nk3 in the ph.x input.

Best regards,
Mitsuaki Kawamura

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Dr. Mitsuaki Kawamura
Software Advancement Team
Supercomputer Section
Materials Design and Characterization Laboratory
The Institute for Solid State Physics, Kashiwa, Japan
e-mail : mkawamura at issp.u-tokyo.ac.jp
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From: developers <developers-bounces at lists.quantum-espresso.org> On Behalf Of Nadeem Muhammad
Sent: Thursday, March 29, 2018 6:34 PM
To: developers at lists.quantum-espresso.org
Subject: [QE-developers] interpolation scheme in the el-ph in PHonon code

Dear
I am Muhammad Nadeem, a master degree student in department of physics at Sungkyunkwan University South Korea. I am working on el-ph calculation of alkali doped organic superconductor. I am using Quantum Espresso code for that. I have some trouble while using electron_phonon='interpolated' in PHonon package. As you can expect that my system is quite large and when I use this interpolation routine even with 2x2x2 q-points and 4x4x4 k-points it gets stuck at electron-phonon stage. My calculation goes very well If I use electron_phonon='simple'. I am using ibrav=0.  Is this happening because interpolation routine does not work in parallel on multiple cpu? Is there some remedy for my problem with this interpolation scheme. As you can expect I can't go for very high number of q-points for dfpt calculation and hence my double delta integration for electron-phonon vertices converges at very high smearing (degauss=0.4Ry) if I use electron_phonon='simple'. Interpolation is the only option left for my calculation. Please give some comments on smearing too. As I understand that this is broadening over electron bands around fermi level so 0.4Ry=5.4eV is too large to give physical electron-phonon coupling parameter. Is it true? if so then please suggest me some solution to tackle this issue.
Looking forward to listen your comments on this issue. Thank you for your time.
Best Regards

Nadeem
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Muhammad Nadeem
Graduate Student
Department of Physics 
Sungkyunkwan University, Suwon