[Wien] How to know if the M+2 has a high spin from calculation?

[Peter Blaha]

It is not always so simple to find the charge state of an atom. It 
really depends on the material you are looking at.

But for Fe 2+ or 3+ in high-spin configuration of some Fe-oxide it is 
rather simple:

Fe3+ in high-spin conf. has 3d5-up and no 3d-dn electrons. This makes a 
spin-moment of 5 per Fe atom (if you have a ferromagnet, you may see 
:MMTOT a multiple of 5, but if it is a ferri or antiferromagnet MMTOT 
may be zero or different). The MMIxxx value of this atom will be large 
(around 4).

If it is Fe 2+, we have 3d5-up/3d1-dn; i.e. only a moment of 4.
The MMIxxx of Fe 2+ is usually around 3.6 muB.

Total charges within an atomic sphere are usually not suitable to decide 
on that.

An alternative is Bades AIM theory and the AIM program can calculate 
these Bader charges. However, also for these Bades charges, the 
differences between Fe 2+ or 3+ might be samll (maybe 0.1 e at most).

So the spin-analysis is best, if you have a high-spin state. Low 
spin-states and/or different symmetries (tetrahedral vs. octahedral,...) 
have different laws and you need some knowledge of crystal field theory 
to get an idea what can happen.



On 08/28/2017 05:11 PM, Fecher, Gerhard wrote:
> Hallo Abderrahmane,
> you find the occupation of the states (INSIDE THE SPERES !) in the case.scf2up/dn files.
> See the lines with e.g.:
> :CHA002: TOTAL VALENCE CHARGE INSIDE SPHERE
> :PCS002: PARTIAL CHARGES SPHERE = 2  .........
> :QTL002: ........
> the content should be selfexplaining.
>
> Take care, you are talking about a model, not about reality.
> Therefore, do not wonder if you do not find integer occupations that you might expect from your chemical model.
>
> You assume that only a certain, integer (!) number of d electrons contribute to the problem (here magnetization)
> but why should this be the absolute and only truth in a solid ?
> Just as an example: Why has bcc Fe a magnetic moment of about 2.2 muB and not exactly 0, 2, or 4 ?
>
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Inorganic and Analytical Chemistry
> Johannes Gutenberg - University
> 55099 Mainz
> and
> Max Planck Institute for Chemical Physics of Solids
> 01187 Dresden
> ________________________________________
> Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von pieper [pieper at ifp.tuwien.ac.at]
> Gesendet: Montag, 28. August 2017 11:10
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] How to know if the M+2 has a high spin from calculation?
>
> No, Wien2k probably won't 'determine alone which spin state is
> energetically more stable'.
>
> States with different spin configurations (PM, FM, AF, ...) frequently
> have small differences in total energy but large differences in their
> electronic configuration. Due to this the scf cycle tends to converge in
> local minima associated with the starting configuration. Thats why you
> should set different spin configurations in lstart and see where the scf
> cycle leads you. The solution with lowest total energy is what you seek.
>
> For your low/high spin configuration this might be enough. There are
> more complicated cases where you may have to guide the scf to the
> correct symmetry by populating the density matrices accordingly - this
> has been discussed in the mailing list a lot - see also option -orbc in
> the UG.
>
> Good luck
>
> Martin Pieper
>
>
> ---
> Dr. Martin Pieper
> Karl-Franzens University
> Institute of Physics
> Universitätsplatz 5
> A-8010 Graz
> Austria
> Tel.: +43-(0)316-380-8564
>
>
> Am 27.08.2017 13:06, schrieb Abderrahmane Reggad:
>> Hello again
>>
>> I have found in the literature that the spin state configuration is
>> like the magnetic configuration. So we have to make 2 calculations:
>> one for the high spin configuration and another one for the low spin
>> configuration and we look after for the configuration more
>> energetically stable.
>>
>> I want to know if the things are so in the wien2k code or it behaves
>> differently and can determine alone which spin state is the more
>> energetically stable.
>>
>> Best regards
>> _______________________________________________
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-- 

                                       P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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