[DFTB-Plus-User] bulk antiferromagnetic Fe2O3 calculation

Ulman Kanchan Ajit kulman at ictp.it
Tue Mar 15 17:15:04 CET 2016

Dear Bálint,

I had used O-O file from the mio set and Fe-O, Fe-Fe from the trans3D set.
I understand that I need to test these well before trusting the results.

I think I'm still not giving correct inputs to describe the magnetic
structure of the antiferromagnetic system I have here. I wish to test some
calculations with dftb and compare them with dft calculations which I
already have.

I have 12 magnetic Fe atoms in the Fe2O3 structure (6 Fe with a magnetic
moment of ~ +4 muB/atom (atom no. 4,5,14,15,24,25) and 6 Fe with a
magnetic moment of ~ -4 muB/atom (atom no. 9,10,19,20,29,30) and O atoms
with no magnetic moments.
The net magnetization is 0, but an absolute magnetization of ~ 48 muB/cell
is expected. So I guess that the parameter UnpairedElectrons should be set
to 0, and the parameter SpinPerAtom for the up Fe atoms should be set to
+0.66667 (4 up electrons of 6) and  -0.66667 for down Fe atoms.

I expect to see that in the detailed.out, the Atom populations for up and
down spin channels should be different depending on the magnetic moment of
Fe atoms.
But I get the same populations of up and down spin for the Fe atoms even
with SpinPerAtom.

Is there a way of specifying the atom populations of Fe atoms, so that I
can specify the no of up and down electrons for each atom.


> One additional note to what I have written before: You did not report,
which SK-set you have used, but if it happens to be the trans3d set (on
top of the mio set), so please keep it mind, that as far as I know, it
was never intended/tested for bulk systems, but was created to describe
single metal atoms in biological complexes. So, make sure, you validate
your results before you start to trust them.
>   Best regards,
>   Bálint
> --
> Dr. Bálint Aradi
> Bremen Center for Computational Materials Science, University of Bremen
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> DFTB-Plus-User at mailman.zfn.uni-bremen.de
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Dr. Kanchan Ulman
Post Doctoral Fellow,
Abdus Salam International Centre for Theoretical Physics,
Strada Costiera 34151, Trieste, Italy.
email: kulman at ictp.it, ulman.kanchan at gmail.com

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