Dear Sir,
I came across a very recent paper by Professor Claudio A. performing DFPT using a nondiagonal supercell method. The section where the fractional kpoints are mapped seems very interesting and appealing. I thus took some time to understand first Professor Monserrat's earlier work on nondiagonal supercell. Using the corresponding .f90 program I was able to get the fractional IBZ (I hope I did correct).
Since there is no tutorial on this, I was wondering how to map now this supercell to get the DFPT results. I would greatly appreciate if you make me understand this process flow.
Thanks and regards,
Sitangshu
About Nondiagonal Supercell and DFPT
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 Posts: 119
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About Nondiagonal Supercell and DFPT
Sitangshu Bhattacharya
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
 claudio
 Posts: 320
 Joined: Tue Mar 31, 2009 11:33 pm
 Contact:
Re: About Nondiagonal Supercell and DFPT
Dear Sitangshu
it is not completely clear to me your question. You can generate nondiagonal supercell that contains a particular phonon mode,
and the paper of B Monserrat presents a strategy to generate the smallest nondiagonal supercell for a given qvector.
Usually, after I generate the nondiagonal supercell, I'm interested in, I use standard DFTP of QuantumEspresso
with only gammapoint to get the phonon modes.
I know that in principle you can map phonon modes from the unit cell to the nondiagonal supercell, but I never wrote
a code to do this, so I prefer to recalculate them.
If it can be useful to you, you can use my python code to generate nondiagonal supercells,
https://github.com/attacc/QEplayground
best regards
Claudio Attaccalite
it is not completely clear to me your question. You can generate nondiagonal supercell that contains a particular phonon mode,
and the paper of B Monserrat presents a strategy to generate the smallest nondiagonal supercell for a given qvector.
Usually, after I generate the nondiagonal supercell, I'm interested in, I use standard DFTP of QuantumEspresso
with only gammapoint to get the phonon modes.
I know that in principle you can map phonon modes from the unit cell to the nondiagonal supercell, but I never wrote
a code to do this, so I prefer to recalculate them.
If it can be useful to you, you can use my python code to generate nondiagonal supercells,
https://github.com/attacc/QEplayground
best regards
Claudio Attaccalite
Claudio Attaccalite
[CNRS/ AixMarseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com
Freely download scientific books from: http://www.freescience.info
[CNRS/ AixMarseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com
Freely download scientific books from: http://www.freescience.info

 Posts: 119
 Joined: Thu Jan 05, 2017 8:08 am
Re: About Nondiagonal Supercell and DFPT
Dear Sir, Thank you for your git link. Actually, I was referring to your paper :https://arxiv.org/pdf/1807.11797.pdf. The para just before the result section seems to be very appealing to us in order to study BSE for fictionalized materials.
Infact we did some work on Tdependent spectra of ML hBN located here: https://arxiv.org/pdf/1811.01695.pdf. I hope the results should be correct.
I am bit confused, or you may say apprehend to solve supercell DFPT+BSE... I don't know if the doublegrid part will map to supercell DFPT calculation (using "iu") or should I not use doublegrid at all for such cases... This is the reason, I never tried this task.
By going through your paper it seems that this could be doable now. That's why I want to learn your methodology.
Let me take some time to go through the link.
Regards,
Sitangshu
Infact we did some work on Tdependent spectra of ML hBN located here: https://arxiv.org/pdf/1811.01695.pdf. I hope the results should be correct.
I am bit confused, or you may say apprehend to solve supercell DFPT+BSE... I don't know if the doublegrid part will map to supercell DFPT calculation (using "iu") or should I not use doublegrid at all for such cases... This is the reason, I never tried this task.
By going through your paper it seems that this could be doable now. That's why I want to learn your methodology.
Let me take some time to go through the link.
Regards,
Sitangshu
Sitangshu Bhattacharya
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
 claudio
 Posts: 320
 Joined: Tue Mar 31, 2009 11:33 pm
 Contact:
Re: About Nondiagonal Supercell and DFPT
Dear Sitangshu
the methodology we use is based on finite differences calculations of electronphonon coupling.
In practice we generate supercells that contain the phonon modes we are interested in, then we move atoms
and calculate the dielectric constant, at the end we average on the different configurations.
Please have a look at these papers:
https://arxiv.org/abs/1512.06377
http://iopscience.iop.org/article/10.10 ... aa737/meta
and also this other one on hBN, where there are much more details, and results similar to ours.
https://arxiv.org/abs/1810.08976
Regarding your results, I think they are correct. The method we use it is different, we calculate electronphonon coupling
by moving atoms and not by direct calculation with QuantumEspresso.
This allows us to include effects not included in standard perturbation theory as for example the phonon replica,
but the price to pay it is to use large supercells
best
Claudio
the methodology we use is based on finite differences calculations of electronphonon coupling.
In practice we generate supercells that contain the phonon modes we are interested in, then we move atoms
and calculate the dielectric constant, at the end we average on the different configurations.
Please have a look at these papers:
https://arxiv.org/abs/1512.06377
http://iopscience.iop.org/article/10.10 ... aa737/meta
and also this other one on hBN, where there are much more details, and results similar to ours.
https://arxiv.org/abs/1810.08976
Regarding your results, I think they are correct. The method we use it is different, we calculate electronphonon coupling
by moving atoms and not by direct calculation with QuantumEspresso.
This allows us to include effects not included in standard perturbation theory as for example the phonon replica,
but the price to pay it is to use large supercells
best
Claudio
Claudio Attaccalite
[CNRS/ AixMarseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com
Freely download scientific books from: http://www.freescience.info
[CNRS/ AixMarseille Université/ CINaM laborarory / TSN department
Campus de Luminy – Case 913
13288 MARSEILLE Cedex 09
web site: http://www.attaccalite.com
Freely download scientific books from: http://www.freescience.info

 Posts: 119
 Joined: Thu Jan 05, 2017 8:08 am
Re: About Nondiagonal Supercell and DFPT
Thank you Sir for your suggestions. I am going through the methodology. Let me see...
Regards,
Sitangshu
Regards,
Sitangshu
Sitangshu Bhattacharya
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/
Indian Institute of Information TechnologyAllahabad
India
Webpage: http://profile.iiita.ac.in/sitangshu/
Institute: http://www.iiita.ac.in/