[QE-users] Help in spin polarized calculation for surface dangling bonds

[Giovanni Cantele]

You need two define two different (but equal) atomic species if you expect
some antiferromagnetic ordering
(thus starting from opposite starting_magnetization on the two).

Usually, if you seek a magnetic solution, you can just set
starting_magnetization to 0.5 or 0.7 and the
self consistent charge density automatically will produce a solution in
which the spin density will be localized only
on the atoms carrying a magnetic moment. So, while you need to
distinguish between atoms with opposite magnetizations,
you shouldn't need, usually, to distinguish between atoms with no net
magnetization and atoms with net magnetization.

I would, at a first glance, try sto set starting_magnetization = 0.7 on all
Si atoms and see what happens.
Giovanni
-- 

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 <giovanni.cantele at spin.cnr.it>
Phone: +39 081 676910
Skype contact: giocan74

ResearcherID: http://www.researcherid.com/rid/A-1951-2009
Web page: https://sites.google.com/view/giovanni-cantele/home


Il giorno sab 19 apr 2025 alle ore 19:46 Lorenzo Sponza <
lorenzo.sponza at onera.fr> ha scritto:

> Thanks Giovanni for your quick answer.
>
> Still, it's not clear to me how to set the starting magnetization.
> Putting just starting_magnetization=X will be useless because this will
> set a starting magnetization in all Si atoms, that will break no
> symmetry.
> On the other hand, if I understood well I can define two atomic species,
> say Si1 and Si2, and define the starting magnetization for only one of
> the two. I think that this is the thing I should do, but I can not
> figure out which atoms should belong to one group or the other and
> wheather I need more than two groups for this specific problem.
> I was hoping to get help from someone who had already done similar
> simulations.
> Cheers
>
> Le 2025-04-19 17:25, Giovanni Cantele a écrit :
> > Dear Lorenzo,
> >
> > the variable starting_magnetization is usually used to drive the
> > system
> > out of the non magnetic solution, in that starting_magnetization(i) =
> > 0 for all atomic species
> > should always bring to a spin unpolarized system. The starting value
> > in some cases is not so important
> > (different values will produce the same magnetic ground state), but as
> > far as I remember it could be
> > in some (not so frequent) cases where different magnetic energy minima
> > exist.
> >
> > For the other questions:
> > - no special attention paid to the pseudopotential choice, if you mean
> > to choose a pseudopotential "specific"
> > for a spin-polarized calculation
> > - I would not use the input_DFT variable unless you need it for
> > specific purposes (e.g. non local functionals, like vdw-DF).
> >
> > Ciao,
> > Giovanni
> >
> > --
> >
> > 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: https://sites.google.com/view/giovanni-cantele/home
> >
> > Il giorno sab 19 apr 2025 alle ore 16:37 Lorenzo Sponza
> > <lorenzo.sponza at onera.fr> ha scritto:
> >
> >> Dear Quantum ESPRESSO users and developpers,
> >>
> >> I need some help to set up a calculation of a Si(111) 1x1 surface.
> >> This
> >> surface is characterized by dangling bonds that spoil the electronic
> >>
> >> states around Fermi. In literature, two approaches are usually
> >> adopted.
> >> One consists in saturating the surface with H atoms, the other
> >> consists
> >> in performing a spin polarized calculation.
> >> I want to give both methods a try, but I stuck when it comes to set
> >> up
> >> the spin polarized input file. I set nspin=2, but I'm perplexed
> >> about
> >> the value to give to starting_magnetization since I have only Si
> >> atoms
> >> here, and in this specific case it is not clear to me how this
> >> variable
> >> is interpreted and used by the code.
> >> Finally, is there any attention to be paid in choosing the
> >> pseudopotential or in specifying the input_DFT variable? I've used
> >> PBE
> >> scalar relativistic PAW pseudos so far.
> >>
> >> Many thanks for your help.
> >>
> >> --
> >> Dr. Lorenzo Sponza
> >>
> >> Chargé de Recherche au CNRS
> >> Université Paris-Saclay, ONERA, CNRS Laboratoire d'étude des
> >> microstructures (LEM)
> >> 29 Avenue de la division Leclerc, 92322 Châtillon
> >> Tel: +33146734464
> >>
> >> ETSF Research Team Leader
> >> European Theoretical Spectroscopy Facility
> >> 17 Sart-Tilman B-4000 Liège, Belgium
> >>
> >
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> --
> Dr. Lorenzo Sponza
>
> Chargé de Recherche au CNRS
> Université Paris-Saclay, ONERA, CNRS Laboratoire d'étude des
> microstructures (LEM)
> 29 Avenue de la division Leclerc, 92322 Châtillon
> Tel: +33146734464
>
> ETSF Research Team Leader
> European Theoretical Spectroscopy Facility
> 17 Sart-Tilman B-4000 Liège, Belgium
>
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