[Wannier] Discrepancy between Wannier90 and DFT band structures

[Azin Kazemi Moridani]

Dear Professor Yates,

Thank you so much for your explanations. I apologize for my late response. There was indeed a discrepancy between the DFT groundstate used to compute the WF and the one used to compute the band structure. After using the same groundstate for both of the calculations, my results improved noticeably. I have included the latest band structures (NC17-modified.png and NC5-modified.png) in the same folder:
https://drive.google.com/drive/folders/1WDjjKl22XXsIW7sdPIbWEsz29ZnkMTGO?usp=sharing
As can be seen, DFT and WF bands completely match for the set of seventeen WF as expected (NC17-modified.png). However, WF bands deviate from that of DFT around the Fermi energy for the set of five WF (NC5-modified.png). Considering I investigated varying an intersection of parameters as mentioned in my previous email, I was wondering if there is a way to improve my results even further, since for my future calculations I need the case with five WF to be precise.

I appreciate your help a lot.

Best Regards,
Mohaddeseh Kazemi-Moridani
Department of Physics,
Université de Montréal

On Apr 14, 2022, at 1:31 PM, Jonathan Yates <jonathan.yates at materials.ox.ac.uk<mailto:jonathan.yates at materials.ox.ac.uk>> wrote:

Hi,

I’ve had a quick look at your files. I can’t say for sure what is wrong with your calculation. But let me make an observation that might help.

Wannier band structures are an interpolation. i.e. when there is no disentanglement (an isolated manifold of bands) at any kpoint that is part of the mesh used to construct the WF, the Wannier interpolated eigenvalues will agree exactly with the original DFT calculation.
The Gamma point should always be part of the mesh used to construct the WF, so the band-structures at Gamma should match.

For the set of 17 WF: Am I right that the DFT bands form an isolated manifold, so no disentanglement is need? If that is true the red and black bands should match at Gamma. They clearly don’t. You need to understand this point before moving on to the set of 5 WF.

[the more I look at NCP17.png I have the feeling that there might be nothing “wrong” with your WF, but that the DFT groundstate used to compute the WF and that used to compute the bands are different in someway e.g. xc functional - just a wild guess..]


Jonathan

On 14 Apr 2022, at 15:48, Azin Kazemi Moridani <mohaddeseh.kazemi.moridani at umontreal.ca<mailto:mohaddeseh.kazemi.moridani at umontreal.ca>> wrote:

Dear All,

I am trying to generate a Wannier90 tight-binding model for Sr2FeO4 using Wannier90 interfaced with ABINIT
. The
overall
behavior
of the bands produced by Wannier90 and ABINIT agree with one another, but there are some discrepancies almost everywhere, especially
around the Fermi energy. I have tried to investigate the effect of varying different parameters, such as : size of the KPOINT mesh, number of iterations, energy window (with and without a frozen window, excluding bands,..), and the set of projections (either
only on Iron d-orbitals, or on Iron d-orbitals plus Oxygen p-orbitals). In the disentangled case of Iron d-orbitals plus Oxygen p-orbitals, the mapping is expected to be exactly on top of the DFT band structure. I performed the calculations with two

pseudopotentials,

Norm-Conserving (NC) and
Projector-Augmented Wave (PAW)
.

In all the cases, convergence is

achieved
but the disagreement persists.


I would appreciate it a lot if anyone could help me improve
my results. The
“wannier90.win<http://wannier90.win>" and "wannier90.wout”
files

alongside the band structures in the case of

five Iron d-orbitals

(NC5.PNG) and
five
Iron d-orbitals plus

twelve (4 * 3) Oxygen p-orbitals (NC17.PNG) can be found here:
https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdrive.google.com%2Fdrive%2Ffolders%2F1WDjjKl22XXsIW7sdPIbWEsz29ZnkMTGO%3Fusp%3Dsharing&data=04%7C01%7Cmohaddeseh.kazemi.moridani%40umontreal.ca%7C3b0b00151b3c4730266708da1e3cc1c8%7Cd27eefec2a474be7981e0f8977fa31d8%7C1%7C0%7C637855544444025253%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Do%2BvZnEhMRqTeavIeXm8EnNIQT8HdpIVIYgdY%2FlKya0%3D&reserved=0


Thank you so much in advance.


Best Regards,
Mohaddeseh Kazemi-Moridani
Department of Physics
Université de Montréal


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