<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">No, it is not necessary if you do not expect that the system under study has a magnetisation.<div class="">See here:</div><div class=""><a href="http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node10.html#SECTION00043030000000000000" class="">http://www.quantum-espresso.org/wp-content/uploads/Doc/pw_user_guide/node10.html#SECTION00043030000000000000</a></div><div class=""><br class=""></div><div class="">In practice, for solids where NO internal or external magnetic field is not present,</div><div class="">time-reversal symmetry applies. This has the consequence that</div><div class=""><br class=""></div><div class="">E(k,up) = E(-k,down)</div><div class=""><br class=""></div><div class="">so for a non-magnetic solid, even in the presence of spin-orbit coupling, it is possible that the spin-up and spin-down</div><div class="">densities are the same and the total magnetisation zero. Non-magnetic solids then can divided into</div><div class="">systems with (spatial) inversion symmetry and systems where this symmetry does not apply.</div><div class=""><br class=""></div><div class="">The former have the additional constraint that E(k, any_spin)=E(-k,any_spin) that, combined with the previous equation,</div><div class="">produces double SPIN degenerate bands (so each state AT GIVEN is at least double degenerate). Germanium is an example.</div><div class=""><br class=""></div><div class="">The latter show a lifting of this double SPIN degeneracy, like in the case of GaAs. The spin degeneracy is recovered ONLY</div><div class="">for those k-points for which k and -k are equivalent (thus differing by only a reciprocal lattice vector). Gamma point is an example.</div><div class=""><br class=""></div><div class="">Giovanni</div><div class=""><br class=""></div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On 16 Nov 2016, at 22:17, ashkan shekaari <<a href="mailto:shekaari@gmail.com" class="">shekaari@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class=""><div class="">Dear experts,<br class=""><br class=""></div>Is starting magnetization necessary to have a full spin-orbit coupling?<br class=""><br class=""></div>What value should it take on?<br clear="all" class=""><div class=""><div class=""><div class=""><div class=""><div class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div dir="ltr" class=""><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><b class="">--</b></span></span></div><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><i style="font-size:12.8px" class="">Regards,</i></span></span></div><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><i class="">Ashkan Shekaari</i></span></span></div><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><i class="">Plasma Physics Research Center</i></span></span></div><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><i style="font-size:12.8px" class=""><span style="font-size:12.8px" class="">Science and Research Branch</span></i></span></span></div><div class=""><span style="" class=""><span style="background-color:rgb(255,255,255)" class=""><i class="">I A U, <span style="font-size:12.8px" class="">14778-93855 Tehran, Iran.</span></i></span></span></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div></div>
</div></div></div></div>
_______________________________________________<br class="">Pw_forum mailing list<br class=""><a href="mailto:Pw_forum@pwscf.org" class="">Pw_forum@pwscf.org</a><br class="">http://pwscf.org/mailman/listinfo/pw_forum</div></blockquote></div><br class=""><div class="">
-- <br class=""><br class="">Giovanni Cantele, PhD<br class="">CNR-SPIN<br class="">c/o Dipartimento di Fisica<br class="">Universita' di Napoli "Federico II"<br class="">Complesso Universitario M. S. Angelo - Ed. 6<br class="">Via Cintia, I-80126, Napoli, Italy<br class="">e-mail: <a href="mailto:giovanni.cantele@spin.cnr.it" class="">giovanni.cantele@spin.cnr.it</a><br class="">Phone: +39 081 676910<br class="">Skype contact: giocan74<br class=""><br class="">ResearcherID: <a href="http://www.researcherid.com/rid/A-1951-2009" class="">http://www.researcherid.com/rid/A-1951-2009</a><br class="">Web page: <a href="http://people.na.infn.it/~cantele" class="">http://people.na.infn.it/~cantele</a><br class="">
</div>
<br class=""></div></body></html>