[Wien] Confusion regarding AFM structure of a spinel compound
Peter Blaha
pblaha at theochem.tuwien.ac.at
Mon Jul 19 12:00:46 CEST 2021
> (1) runsp_lapw -dm -orb -fc 1.0 -ec 0.0001 -min
> (2) Taking the optimized structure from the previous run, I have started
> force minimization by min-j" runsp_lapw ......
> (3) I have copied the final structure as has been obtained in the force
> minimization & take it to a different directory for simulating the
> energy of the compound.
> (4) By taking the force minimized structure I have run runsp_lapw -dm
> -orb -fc 1.0 -ec 0.0001 -cc 0.0001
>
> Please suggest to me if I am doing something wrong.
Almost "everything".
ad 1) -dm not necessary (-orb will set it automatically); -min DOES
already a force minimization !!!
ad 2) completely unnecessary when you have -min in 1)
ad 3) from what you wrote, you only copied case.struct. I'd never do
that, see below.
ad 4) before you can runsp ..., what have you done ?? You need an
initialization with AFM setup, init_orb
What you should do (asuming you have a proper initialization):
1) runsp_lapw -orb -fc 1.0 -ec 0.0001 -min # check final forces,
otherwise rerun command 1)
2) save_lapw relaxed
In case you really want to run another scf in a new directory with the
relaxed structure:
3) mkdir new; cp relaxed.* new; cd new; restore_lapw relaxed
4) runsp_lapw -orb -fc 1.0 -ec 0.0001
step 4 should stop after 3 cycles.
>
> warm regards,
>
>
> On Mon, 19 Jul 2021 at 14:47, Peter Blaha <pblaha at theochem.tuwien.ac.at
> <mailto:pblaha at theochem.tuwien.ac.at>> wrote:
>
> > I am working on a frustrated AFM ordering in
> which
> > both the atom with spin up & spin down remains at the octahedral
> site. I
> > have simulated the same structure with U=4 eV & which works well.
> > However, when I shifted to U=6 eV the structure showed AFM during
> > structure optimization while the magnetic moment didn't cancel
> when I go
> > for an SCF with the optimized structure.
>
> When you do "structure optimization (whatever you actually mean by
> that
> ... ?)" you actually do for sure a scf calculation also for the
> optimized structure. So it seems to work....
>
> You did not explain what you have done at: "I go for an SCF with the
> optimized structure".
> Apparently here you have done something which breaks AFM (it is easy to
> get some arbitrary magnetic state in DFT+U when one is not careful with
> dmat* or vorb* files)..
>
>
>
> >
> > with regards,
> >
> > On Mon, 19 Jul 2021 at 14:32, Laurence Marks
> <laurence.marks at gmail.com <mailto:laurence.marks at gmail.com>
> > <mailto:laurence.marks at gmail.com
> <mailto:laurence.marks at gmail.com>>> wrote:
> >
> > Without the struct nobody can do more than guess.
> >
> > My guess. In spinel you have any octahedral & tetrahedral
> sites. You
> > put one spin (Up) on octahedral sites, and the other (Dn) on
> > tetrahedral. This won't work.
> >
> > _____
> > Professor Laurence Marks
> > "Research is to see what everybody else has seen, and to
> think what
> > nobody else has thought", Albert Szent-Györgyi
> > www.numis.northwestern.edu <http://www.numis.northwestern.edu>
> <http://www.numis.northwestern.edu <http://www.numis.northwestern.edu>>
> >
> > On Mon, Jul 19, 2021, 03:23 shamik chakrabarti
> > <shamik15041981 at gmail.com <mailto:shamik15041981 at gmail.com>
> <mailto:shamik15041981 at gmail.com <mailto:shamik15041981 at gmail.com>>>
> wrote:
> >
> > Dear Wien2k users,
> >
> > I was running AFM calculation of a
> spinel
> > compound by flipping the spin in case.inst & by running spin
> > polarize calculation. During structure optimization, the AFM
> > structure appears well with zero moments per unit cell.
> However,
> > when I have started an SCF by taking the
> optimized structure the
> > calculation converges in 50 iterations with a moment ~ 8
> muB/per
> > unit cell. Also, the atoms which are connected with AFM
> ordering
> > do not show equal moments with opposite directions. The
> > moment of an atom is 2.7muB while the atom connected with AFM
> > ordering showed a moment of -0.77 muB.
> >
> > The convergence criteria was set as: -ec 0.0001, -cc
> 0.0001, fc
> > 1.0 & the calculation converges in 50 iterations.
> >
> > I have set 14 k-points for 56 atomic cells & also using GGA+U
> > with U=6 eV for the TM atom.
> >
> > Any response in this regard will be helpful for us.
> >
> > Thanks in advance,
> >
> > with regards,
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
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> >
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> >
> >
> >
> > --
> > Dr. Shamik Chakrabarti
> > Research Fellow
> > Department of Physics
> > Indian Institute of Technology Patna
> > Bihta-801103
> > Patna
> > Bihar, India
> >
> > _______________________________________________
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> >
>
> --
> Peter Blaha, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
> Phone: +43-1-58801-165300 Email: peter.blaha at tuwien.ac.at
> <mailto:peter.blaha at tuwien.ac.at>
> WWW: http://www.imc.tuwien.ac <http://www.imc.tuwien.ac>
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>
>
> --
> Dr. Shamik Chakrabarti
> Research Fellow
> Department of Physics
> Indian Institute of Technology Patna
> Bihta-801103
> Patna
> Bihar, India
>
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--
Peter Blaha, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300 Email: peter.blaha at tuwien.ac.at
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