[Wien] Confusion regarding AFM structure of a spinel compound

[Peter Blaha]

>                    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>> 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>
> 
>     On Mon, Jul 19, 2021, 03:23 shamik chakrabarti
>     <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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> 
> 
> -- 
> 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