[Wannier] Kramers degeneracy broken by Wannier interpolation

[Antimo Marrazzo]

On 06/21/2017 02:32 PM, Aguilera, Irene wrote:
> ...
> For those q points there is a small splitting between the Kramers 
> partners. So, I think I understand why this happens and I understand 
> how to improve it and make the splitting negligible (increasing the k 
> points in the DFT calculation does it).
Dear Irene,

increasing the DFT k-points grid helps for sure, but (if you are using 
disentanglement) playing with the windows (especially the frozen ones) 
may actually help a lot (and keeping a coarse k-points grid will help 
you with GW). Typically in a good (converged minimization, low spreads) 
wannierization that effect should be negligible, even with rather coarse 
k-points grids.

> But I cannot find a solution to obtain real degeneracies and I could 
> not find discussions about this issue in the literature or in the forum.
>
> Are there approaches to solve this problem? How can one symmetrize 
> H(q)? Can one impose some conditions on H(R) (the Hamiltonian in real 
> space) such that H(q) presents the correct symmetries?
In general yes, look at the work of R. Sakuma 
https://doi.org/10.1103/PhysRevB.87.235109 on symmetry-adapted MLWF and 
examples 21-22 of the latest W90 release.

HTH,

Antimo

-- 
Antimo Marrazzo
Doctoral Assistant
EPFL STI IMX THEOS
ME-D2 1019 (Bâtiment ME)
Station 9
CH-1015 Lausanne (Switzerland)

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