Tutorial: symmetrization

[jaemolihm]

https://github.com/wannier-berri/Wannier2022/blob/main/advanced/symmetrization/Symmetrization_tutorial.ipynb

From email discussion with Xiaoxiong:

in Fe calculation, the BCD show small wiggles even after symmetrization. What is the reason for this?

Small wiggles and high peaks comes from the results are not converged with low-density k-grid around band intersection or small gaps.

But I am still confused. If the model is perfectly symmetric, shouldn't the bcd be 0 due to cancellation between k and -k?

[Liu-Xiaoxiong]

Thanks for pointing out it and pushing me to think more about it.
Yes, you are right. it should be zero.

The conclusion from my side is: that it is a digital error from MixFT.

If you set NKFFT = 1. most of the sharp peaks are gone.

I tabulate Der_berry on an NK=10 grid. Der_berry from each +k and -k can match up to e-7. (so some small wiggles may be from digital error as well)

[jaemolihm]

The variable name Fe_sym_Morb should be Fe_sym_BCD.

[Liu-Xiaoxiong]

Done thanks.

[Liu-Xiaoxiong]

@jaemolihm @stepan-tsirkin
I know why !!! Respect to Jaemo's questions about running more than once ''symmetrization" can have a more beautiful zero.

The orbital arrangement in VASP-Wannier data and QE-Wannier data.
Eg: if we write Te: s;p in the projection card in wannier90.win. (with SOC)
The arrangement of vasp is [s,pz,px,py,s,pz,px.py] but arrangement of qe is [s,s,pz,pz,px,px,py,py].

I write the code based on VASP arrangement. So all the input matrixes should rearrange to vasp version and start the symmetrization steps. I didn't rearrange back after symmetrization.

So if you run more than once symmetrization now, the orbital cannot match the orbital rotation matrix from the second symmetrization. Then all the matrix elements are going to zero.

Use the master version. First symmetrization with DFT_code = 'qe'. Then run with DFT_code = 'vasp', no mater how many time you run symmetrization, there always have a peak at some energy. But Amplitude will change after each symmetrization. (This behaves like digital error)

Do you agree?

I am going to fix the bug soon! After that, you can always run symmetrization with 'qe' for qe-wannier90 data as much as you want.

Thanks

[Liu-Xiaoxiong]

I only rearrange back the data. BCD result of Fe looks better accidentally.
I believe it is an accident. Because if we run more than once symmetrization step. We can see some higher peaks.