[Pw_forum] SPIN

[Giovanni Cantele]

No, it is not necessary if you do not expect that the system under study has a magnetisation.
See here:
http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node10.html#SECTION00043030000000000000 <http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node10.html#SECTION00043030000000000000>

In practice, for solids where NO internal or external magnetic field is not present,
time-reversal symmetry applies. This has the consequence that

E(k,up) = E(-k,down)

so for a non-magnetic solid, even in the presence of spin-orbit coupling, it is possible that the spin-up and spin-down
densities are the same and the total magnetisation zero. Non-magnetic solids then can divided into
systems with (spatial) inversion symmetry and systems where this symmetry does not apply.

The former have the additional constraint that E(k, any_spin)=E(-k,any_spin) that, combined with the previous equation,
produces double SPIN degenerate bands (so each state AT GIVEN is at least double degenerate). Germanium is an example.

The latter show a lifting of this double SPIN degeneracy, like in the case of GaAs. The spin degeneracy is recovered ONLY
for those k-points for which k and -k are equivalent (thus differing by only a reciprocal lattice vector). Gamma point is an example.

Giovanni


> On 16 Nov 2016, at 22:17, ashkan shekaari <shekaari at gmail.com> wrote:
> 
> Dear experts,
> 
> Is starting magnetization necessary to have a full spin-orbit coupling?
> 
> What value should it take on?
> --
> Regards,
> Ashkan Shekaari
> Plasma Physics Research Center
> Science and Research Branch
> I A U, 14778-93855 Tehran, Iran.
> _______________________________________________
> Pw_forum mailing list
> Pw_forum at pwscf.org
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-- 

Giovanni Cantele, PhD
CNR-SPIN
c/o Dipartimento di Fisica
Universita' di Napoli "Federico II"
Complesso Universitario M. S. Angelo - Ed. 6
Via Cintia, I-80126, Napoli, Italy
e-mail: giovanni.cantele at spin.cnr.it
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: http://people.na.infn.it/~cantele

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