[Pw_forum] SPIN

[ashkan shekaari]

Dear Giovanni Cantele,

Thank you so much for the detailed response. As my last question, what is
the exact difference between starting magnetization and total magnetization?

*--*
*Regards,*
*Ashkan Shekaari*
*Plasma Physics Research Center*
*Science and Research Branch*
*I A U, 14778-93855 Tehran, Iran.*

On Thu, Nov 17, 2016 at 2:16 PM, Giovanni Cantele <
giovanni.cantele at spin.cnr.it> wrote:

> 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
>
> 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.*
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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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