the starting magnetisation is provided as input variable, as detailed here: http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm6316208 <http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm6316208> and is needed to break the symmetry and allow pw.x to search for a magnetic solution with energy lower that the non magnetic one, if it exists. So, even in absence of spin-orbit coupling, if you want to study a magnetic ground state of a certain material, you have to provide it in input to trigger the spin-polarised calculation.
The total magnetisation is instead used to impose a specific magnetisation on your system: http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm6318192 <http://www.quantum-espresso.org/wp-content/uploads/Doc/INPUT_PW.html#idm6318192> instead of allowing pw.x to determine it during the self-consistent cycle. Of course, if you impose something it is not guaranteed that you are studying the lowest energy configuration. Giovanni > On 17 Nov 2016, at 14:24, ashkan shekaari <[email protected]> wrote: > > 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 > <[email protected] <mailto:[email protected]>> 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 > > <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 <[email protected] >> <mailto:[email protected]>> 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 >> [email protected] <mailto:[email protected]> >> http://pwscf.org/mailman/listinfo/pw_forum >> <http://pwscf.org/mailman/listinfo/pw_forum> > -- > > 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: [email protected] <mailto:[email protected]> > Phone: +39 081 676910 > Skype contact: giocan74 > > ResearcherID: http://www.researcherid.com/rid/A-1951-2009 > <http://www.researcherid.com/rid/A-1951-2009> > Web page: http://people.na.infn.it/~cantele > <http://people.na.infn.it/~cantele> > > > _______________________________________________ > Pw_forum mailing list > [email protected] <mailto:[email protected]> > http://pwscf.org/mailman/listinfo/pw_forum > <http://pwscf.org/mailman/listinfo/pw_forum> > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum -- 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: [email protected] 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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