[Pw_forum] SPIN

[Lorenzo Paulatto]

On Thursday, November 17, 2016 12:47:16 AM CET ashkan shekaari wrote:
> Dear experts,
> 
> Is starting magnetization necessary to have a full spin-orbit coupling?
> 
> What value should it take on?

I'm not 100% sure, normally you need a starting_magnetization to break the 
initial time reversal symmetry and allow the system to polarize, however if 
I'm not wrong, this is breaking of symmetry is always present when using full-
relativistic pseudopotentials with spin orbit coupling (are you?)

Anyway, it is just a starting value and the system *should* converge to the 
the same ground state regardless of the choice. Just set it to some small 
numbe, i.e. 0.01 and have a try.

Not that starting_magnetization is defined per atomic *species* not per atom, 
and it goes from 0 (atom is non-magnetic) to 1 (the atom is as polarized as 
possible in its isolated atom configuration).

I try to clarify with an example.  Let's say you have an Oxygen atom, with 
valence configuration 2s2 2p4. If you set starting_magnetization=0, then the 2 
2s electrons will be one spin up and one spin down, the 4 2p electrons will be 
2 spin up and 2 spin down, total=0. If you set starting_magnetization=1, then 
the 2s electrons will still be one up and one down, because there is no other 
way to do it, but the 2p electrons will be 3 spin up and 1 spin down, for a 
total magnetic moment of 2 Bohr magnetons

hth



-- 
Dr. Lorenzo Paulatto 
IdR @ IMPMC -- CNRS & Université Paris 6
phone: +33 (0)1 44275 084 / skype: paulatz
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