[Wien] Treating 4f states as core

[Laurence Marks]

Treating the Ln atoms as core ignores the crystal field splitting. In my
opinion it is an approximation used in to get the calculation to converge,
except for La & Gd I cannot justify it.

The Hubbard +U puts the 4f very low in energy, in effect "shoves them out
of the way". Based upon our analysis in DOI:
10.1103/PhysRevMaterials.2.025001 it is not right in many cases, rather a
pragmatic approximation to get converged results which are insulators.

Based upon the paper on YbFeO3, which is experiment, the Yb are "up" and
the Fe are "down" if I have read it right. If you replace Yb with Sc, since
Sc3+ is non-magnetic I would expect the Fe spins to remain the same and the
system will be ferromagnetic.

There are probably many papers where people have done calculations on
systems such as this and obtained physically unreasonable or incorrect
results.

On Thu, Apr 9, 2020 at 10:01 AM Ali Baghizhadeh <ali.baghizhadeh at ua.pt>
wrote:

> Dear Prof. Laurence
> Thank you. In the mentioned paper, they treated Yb 4f electrons  as
> valance while some for HoMnO3 or DyFeO3, treated 4f electrons as core. I do
> not know what is the best approach?
> For most h-LuFeO3 family there is experimentally a weak FM, and there are
> some ideas on its origin, while the lattice is AFM. For YbFeO3, I did
> similar calculation like the paper you are quoting, and it is AFM. When I
> do doping with Sc (4 Sc and 2 Yb ions), it always switches to FM.
> Bets regards.
> Ali
>
> ------------------------------
> *From:* Wien <wien-bounces at zeus.theochem.tuwien.ac.at> on behalf of
> Laurence Marks <laurence.marks at gmail.com>
> *Sent:* Thursday, April 9, 2020 1:58 AM
> *To:* A Mailing list for WIEN2k users <wien at zeus.theochem.tuwien.ac.at>
> *Subject:* Re: [Wien] Treating 4f states as core
>
> Let me turn this thread around a bit, as it seems to be endless. There are
> several possible reasons you are not getting an AFM solution, the two main
> ones being:
> a) You are doing the calculation wrong.
> b) It is not AFM.
>
> What is the evidence that it should be AFM? Your opinion, or
> uncontroversial experimental evidence?
>
> Based on DOI: 0.1103/PhysRevB.95.224428 it is not AFM!
>
> _____
> Professor Laurence Marks
> "Research is to see what everybody else has seen, and to think what nobody
> else has thought", Albert Szent-Gyorgi
> www.numis.northwestern.edu
>
>
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-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: www.numis.northwestern.edu/MURI
Co-Editor, Acta Cryst A
"Research is to see what everybody else has seen, and to think what nobody
else has thought"
Albert Szent-Gyorgi
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