GW vs GGA band gap
Moderators: myrta gruning, andrea marini, Daniele Varsano, Conor Hogan
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Re: GW vs GGA band gap
Dear Daniele,
What's his name and where could I find it ?
Best,
Lamia
What's his name and where could I find it ?
Best,
Lamia
Taouil Lamia
University of Mohammed V
Faculty of science - Rabat
Morocco
University of Mohammed V
Faculty of science - Rabat
Morocco
- Daniele Varsano
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Re: GW vs GGA band gap
Dear Taouil,
these are the files containing the band output (o.bands*), where are you looking the gap?
Note that the gap reported in the report indicated with X " [X]Indirect Gaps" is always the KS gap, so you cannot see the GW gap from there, but you need to inspect the bands output.
Best,
Daniele
these are the files containing the band output (o.bands*), where are you looking the gap?
Note that the gap reported in the report indicated with X " [X]Indirect Gaps" is always the KS gap, so you cannot see the GW gap from there, but you need to inspect the bands output.
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
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- Posts: 68
- Joined: Mon Dec 05, 2016 5:09 pm
Re: GW vs GGA band gap
Dear Daniele,
Thank you so much for your comment. Could you give me more details about it, please?
Regards,
Lamia
Thank you so much for your comment. Could you give me more details about it, please?
Regards,
Lamia
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Taouil Lamia
University of Mohammed V
Faculty of science - Rabat
Morocco
University of Mohammed V
Faculty of science - Rabat
Morocco
- Daniele Varsano
- Posts: 3838
- Joined: Tue Mar 17, 2009 2:23 pm
- Contact:
Re: GW vs GGA band gap
Dear Lamia,
looking at your bands (see plot) you can recognise that the direct gap at gamma is about 2.58eV which correspond to the GW gap you find in the o.qp file:
So, the GW corrections are taken into account.
Best,
Daniele
looking at your bands (see plot) you can recognise that the direct gap at gamma is about 2.58eV which correspond to the GW gap you find in the o.qp file:
Code: Select all
1.000000 4.000000 -1.466253 -1.278971 0.187282 0.743058
1.000000 5.000000 0.300217 1.299281 0.999064 0.762584
Best,
Daniele
You do not have the required permissions to view the files attached to this post.
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
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- Posts: 68
- Joined: Mon Dec 05, 2016 5:09 pm
Re: GW vs GGA band gap
Dear Daniele ,
how could I read the value of band gap from o.qp?
and actually my structure has an indirect band gap with 2.43 eV wich doesn't correspond to what was found? could you suggest any solution for that?
best,
Lamia
how could I read the value of band gap from o.qp?
and actually my structure has an indirect band gap with 2.43 eV wich doesn't correspond to what was found? could you suggest any solution for that?
best,
Lamia
Taouil Lamia
University of Mohammed V
Faculty of science - Rabat
Morocco
University of Mohammed V
Faculty of science - Rabat
Morocco
- Daniele Varsano
- Posts: 3838
- Joined: Tue Mar 17, 2009 2:23 pm
- Contact:
Re: GW vs GGA band gap
Dear Lamia,
in the o.qp you have the KS energies and their GW correction for all the points you have calculated.
From that you can extract your indirect band gap.
What is the 2.43 eV value? If this is the experimental gap, there could be many reason why the GW gap is different:
1. Convergence parameters
2. G0W0 starting DFT ground state i.e. absence of self consistency
3. strongly correlated system...
and so on...
Best,
Daniele
in the o.qp you have the KS energies and their GW correction for all the points you have calculated.
From that you can extract your indirect band gap.
What is the 2.43 eV value? If this is the experimental gap, there could be many reason why the GW gap is different:
1. Convergence parameters
2. G0W0 starting DFT ground state i.e. absence of self consistency
3. strongly correlated system...
and so on...
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
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- Posts: 68
- Joined: Mon Dec 05, 2016 5:09 pm
Re: GW vs GGA band gap
Dear Daniele,
Could you explain more the second and third points, please?
and witch parameters correspond to them?
ps: The system is 2D
regards,
Lamia
Could you explain more the second and third points, please?
and witch parameters correspond to them?
ps: The system is 2D
regards,
Lamia
Taouil Lamia
University of Mohammed V
Faculty of science - Rabat
Morocco
University of Mohammed V
Faculty of science - Rabat
Morocco
- Daniele Varsano
- Posts: 3838
- Joined: Tue Mar 17, 2009 2:23 pm
- Contact:
Re: GW vs GGA band gap
Dear Lamia,
I just wanted to say that there could be many reason why GW does not predict the experimental gap of a materials.
It is a powerful theory but it also has limitations: see e.g.
https://onlinelibrary.wiley.com/doi/abs ... /wcms.1344
Now, I do not know what system you are dealing with, so I cannot say much. Maybe you can have a look if there are other GW calculations on your system in the literature and compare with them. Of course, careful converge tests are mandatory.
Best,
Daniele
PS: if the system is 2D there is a strong dependency on the vacuum size and you are surely underestimating your gap. In order to mitigate this issue you should use truncated coulomb potential. You can have a look to the yambo tutorial on how to use them.
I just wanted to say that there could be many reason why GW does not predict the experimental gap of a materials.
It is a powerful theory but it also has limitations: see e.g.
https://onlinelibrary.wiley.com/doi/abs ... /wcms.1344
Now, I do not know what system you are dealing with, so I cannot say much. Maybe you can have a look if there are other GW calculations on your system in the literature and compare with them. Of course, careful converge tests are mandatory.
Best,
Daniele
PS: if the system is 2D there is a strong dependency on the vacuum size and you are surely underestimating your gap. In order to mitigate this issue you should use truncated coulomb potential. You can have a look to the yambo tutorial on how to use them.
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
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- Posts: 68
- Joined: Mon Dec 05, 2016 5:09 pm
Re: GW vs GGA band gap
Dear Daniele ,
The system is SnC -2D
best,
Lamia
The system is SnC -2D
best,
Lamia
Taouil Lamia
University of Mohammed V
Faculty of science - Rabat
Morocco
University of Mohammed V
Faculty of science - Rabat
Morocco
- Daniele Varsano
- Posts: 3838
- Joined: Tue Mar 17, 2009 2:23 pm
- Contact:
Re: GW vs GGA band gap
OK, but I think it is your job to understand what is going on.
Please have a look to my comment above about treating the interaction in 2D system, you need to use truncated coulomb potential to avoid spurious interaction among images.
Best,
Daniele
Please have a look to my comment above about treating the interaction in 2D system, you need to use truncated coulomb potential to avoid spurious interaction among images.
Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/