[Wannier] [SUSPECT ATTACHMENT REMOVED] PW vs Wannier interpolated bandstructure of Silicon

[Samuel Ponce]

Dear Wannier team,

I have a small question about Wannier90.

Somehow I find it very difficult to get very good Wannierization of Silicon. I'm interested in the top of the VB and the bottom of the CB (between G-X).

I can get okish one but when I try to improve them, I do not manage.

Attach to this email is a comparison between the L-G-X path of Silicon with PW/bands.x (in green) VS Wannier90 in red.

As you can see, the Wannier code fail to reproduce the second branch of the CBM (on the right), which is problematic. The wannier seems to have some unphysical oscillation in the CB.

Attach to this email are all the file needed to obtain both plots and even the line needed to do the gnuplot (you have to scale them). In each of them I've place a README file with all the steps for convenience. I've also placed the psp.
The calculations are very fast.

Maybe its something very stupid.

So far, I've try:
- increasing the nscf grid (you can see a comparison between 8x8x8 and 10x10x10 grid. The latest 10x10x10 gives dramatic oscillations)
- changing the number of bands
- playing with the frozen windows
- increasing the number of Wannier iteration

Nothing made it better than that.

Would you have any suggestions?

PS: The lattice parameter is slightly lower (10.17 Bohr) than the DFT one (10.208 Bohr) on purpose but is the same in both case. In the case of the DFT lattice 10.208 similar issues exists but its slightly better.

PPS: I also noticed that the Wannierzation was breaking the symmetries. For example doubly degenerate bands along G-X were slightly lifted. As a results, effective masses are quite bad. Is there a way to impose crystal symmetries?

Thank you,

Samuel
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