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Topological invariant calculation for large system with only gamma kpoint
Date: 2020/07/20 10:50
Name: Frank

Hi everybody,
I want to calculate the topological features of a very large system with about 200 atoms or even more in the unit cell, which I think I will only use gamma point.
I am wondering whether the method of calculating topological invariant newly implemented in openmx can deal with the gamma point calculation.
If not, do you have any advice to do with the topological features of a very large system?
I appreciate that anyone can help.

Thank you very much.

Best,
Frank
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Re: Topological invariant calculation for large system with only gamma kpoint ( No.1 )
Date: 2020/07/27 11:10
Name: Hikaru Sawahata  <sawahata@cphys.s.kanazawa-u.ac.jp>

Hi Frank,

Is this a Z2 invariant? Or Chern number? Or others?
>The topological features

My opinion is we cannot calculate the topological invariant in most cases only Gamma point.
However, only Z2 topological invariant cases, we may be able to compute it by low computational cost.
Z2 invariant of the system with inversion symmetry can be evaluated by parity signs on time reversal invariant k-points.
Please see this article.
https://doi.org/10.1103/PhysRevB.76.045302

Regards,

Kanazawa University
Hikaru Sawahata
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Re: Topological invariant calculation for large system with only gamma kpoint ( No.2 )
Date: 2020/07/27 11:46
Name: Fumiyuki Ishii

Hi Frank

After computing SCF calculation by Gamma point, you can compute topological invariants by increasing k-point in post processing code of computing Z2 or Chern number.
Please check k-point convergence for not SCF but post processing code.

Regards,
Fumiyuki Ishii
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