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Z2PackDev / Z2Pack

A tool for calculating topological invariants.
https://z2pack.greschd.ch
GNU General Public License v3.0
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WCC are not degenrate Kramers pair at the edges of the surface #215

Open sharm608 opened 3 months ago

sharm608 commented 3 months ago

Dear developer,

I am calculating the z2 invariant of a 2D system with tight binding Hamiltonian. The Hamiltonian is complex conjugate and time reversal invariant. When I calculate z2 invariant it gives WCC are not degenerate Kramers pairs at the edges of the surface.
The values of WCC at the edges are close but have some difference. Upon reducing the pos_tol (say pos_tol = 0.00001) the difference in WCC reduces and the issue is somewhat mitigated. Please let me know what could be going wrong.

Many thanks, Shivam

greschd commented 3 months ago

How was the tight-binding Hamiltonian generated? The easiest explanation would be that there is a small numerical difference already there.

shahid-sattar commented 2 months ago

Hi @sharm608, have you been able to fix this issue? I am also trying to compute Z2 invariant for a 2D system and getting around some errors. Let me know if it works in your case.