[QE-users] Spin projections not working OR (more probable) really dumb misunderstanding

[Thomas Brumme]

Dear all,

I'm calculating the full-relativistic band structure of some WSe2 
nanotubes which works fine and also the band structure agrees with 
calculations done with FHI-aims (which I have to use for larger systems).
In order to understand some interesting feature in the band splitting 
I'm also calculating the expectation values of the spin operators using 
bands.x and setting lsigma(1..3) to .true.

Yet, for some of the bands all expectation values are zero. I don't 
understand this. OK, I know that only the total angular momentum is 
conserved and spin is not a good quantum number anymore but does this 
also mean that the expectation value for the "spin vector" can be zero? 
I had a similar problem in the past for a monolayer WSe2 and there the 
spin was also not really 1/2 anymore which might actually be a 
DFT-specific problem as far as I understood it after discussing with 
other colleagues. But zero?

Kind regards

Thomas Brumme

-- 
Dr. rer. nat. Thomas Brumme
Theoretical chemistry
TU Dresden - KOE / 103
Bergstr. 66c
01069 Dresden

Tel:  +49 (0)351 463 40844

email: thomas.brumme at tu-dresden.de