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

[Thomas Brumme]

OK, I retract the question... It is really dumb. One just has to think a 
bit about what "expectation value" really means.

Anyways, cheerio

Thomas

On 7/7/22 15:03, Thomas Brumme wrote:
> 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