WCC are not degenrate Kramers pair at the edges of the surface

[sharm608]

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]

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

[shahid-sattar]

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.