[Wien] Confusion regarding AFM structure of a spinel compound
shamik chakrabarti
shamik15041981 at gmail.com
Mon Jul 19 14:33:48 CEST 2021
Dear Prof. Blaha,
Thank you for your advice. However, I have few
queryes. For a big cell-like 56 atomic cell semiconductor, can I consider 4
k points during structure optimization while 14 k-points during energy
calculation with the optimized structure (*the step 4*)? If I really need
to increase the k-points at the step 4 what should I do?.an initialization
with 14 k-points ??
with regards,
On Mon, 19 Jul 2021 at 15:30, Peter Blaha <pblaha at theochem.tuwien.ac.at>
wrote:
> > (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>
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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
> WWW: http://www.imc.tuwien.ac WIEN2k: http://www.wien2k.at
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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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