[Wannier] Discrepancy between Wannier90 and DFT band structures

[Jonathan Yates]

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> 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" 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://drive.google.com/drive/folders/1WDjjKl22XXsIW7sdPIbWEsz29ZnkMTGO?usp=sharing
> 
> 
> Thank you so much in advance.
> 
> 
> Best Regards,
> Mohaddeseh Kazemi-Moridani
> Department of Physics
> Université de Montréal
> 
> 
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