[Wien] Confusion regarding AFM structure of a spinel compound

[shamik chakrabarti]

Dear Prof. Marks,

                  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.

with regards,

On Mon, 19 Jul 2021 at 14:32, Laurence Marks <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
>
> On Mon, Jul 19, 2021, 03:23 shamik chakrabarti <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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