[QE-users] Expectation values of total angular momentum in SOC case

[Lorenzo Paulatto]

Hello Thomas,
if I remember correctly, the fact that the spin does not commute with 
the Hamiltonian mean that the spin can be:
1. k-point dependent, you do not have spin-up and spin-down bands which 
can be separated
2. aligned along any direction, instead of just Z

I think, but am not 100% sure, that if J is a good quantum number for 
isolated atoms with mean-field interacting electrons, this is not true 
for bulk crystals (what is L in the bulk?)

With the options of bands.x setting lsigma=.true. you can plot the spin 
projected over x y and z and do some kind of color-codes plot of the bands

cheers



On 22/01/2020 16:57, Thomas Brumme wrote:
> Dear all,
> 
> I tried to find something in the archive but was not successful.
> 
> In noncollinear calculations I can plot the spin expectation values 
> using bands.x.
> Those are calculated using the standard Pauli matrices. Yet, spin is not 
> a good
> quantum number anymore once I have SOC. Thus, I actually have to look at 
> the
> total angular momentum, J. Is it possible to get the expectation values 
> of J?
> Does it make sense at all to think about implementing it?
> 
> Regards
> 
> Thomas
> 

-- 
Lorenzo Paulatto - Paris