[Wien] What's the meaning of "up" and "down" in a band structure including spin-orbit interaction?

[archieve mail]

Dear Prof. Blaha,

    I have two question about spin-orbit calculation.
    As far as I know, the spin-up and spin-down states will coupling
together, and the direction of spin angular moment can rotate in the three
dimension space, if spin-orbit coupling is included in the DFT Hamiltonian.
In a usual pseudopotential code, non-collinear spin is necessary to do a
spin-orbit interaction. My question is:

1. It looks like wien2k does not need non-collinear spin to do a spin-orbit
coupling calculation. Why?

2. What's the meaning of spin-up and spin-down in a band structure
including spin-orbit interaction?

Thanks a lot.


Best Regards,

Yonghong
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