[Wien] magnetism calculation in Wien2K

[Stefaan Cottenier]

This will be far from the definitive answer, but if you ask which (NM  
or FM) would be the better crude approximation for a paramagnetic  
state, I would guess it depends on the quantity you are interested in.

What I am sure about: very local quantities (such as interatomic  
distances, and the EFG which can be sometimes very much dependent on  
them) in a a PM are better described by the FM solution.

What I am just guessing: properties that are more of an averaged  
nature (can we consider lattice constants as an example?) could be  
better described by the NM solution.

I vaguely remember to have had a case which was definitely  
(experimentally) a paramagnet, and the FM total energy was lower than  
the NM one. There the disorder of the moments introduced only a minor  
effect on the total energy. But I'm not sure how general this is.

Stefaan


Quoting villesuzanne <ville at icmcb-bordeaux.cnrs.fr>:

> Dear Stefaan,
>
> The paramagnetic case is an interesting, very basic issue to discuss here.
>
> Non spin-polarized calculations are often referred as "non-magnetic" in
> literature, since obviously there is no resulting magnetic moment nor spin
> density (both spin channels have the same electron density).
>
> If I am right (not an expert in magnetism), a paramagnetic phase has
> well-defined local magnetic moments, for example on transition metal ions,
> and these moments are disordered.
>
> Therefore, although the macroscopic magnetization is zero in a paramagnet
> (without an external field), the spin-polarized (FM) solution is maybe a
> better approximation for a paramagnet: Only spin-polarized calculations will
> give a net magnetic moment on the magnetic ion.
>
> The non-magnetic approximation of a paramagnet is equivalent to define it as
> a metallic system (with not even local magnetic moments), that becomes
> magnetic under application of a magnetic field.
>
> Definitely, a paramagnet cannot be described exactly by a periodic
> calculation. But what is the better crude approximation, NM or FM ?
>
> Regards,
> Antoine
>
>
>
> In other words,
>>      How to distinguish the paramagnetism (PM),
>> ferromagnetism (FM) and
>> antiferromagnetism (AFM) of materials, besides the
>> comparing the
>> their total energies?
>
> Comparing total energies is usually the way to go. You might play with
> the non-collinear code to find the orientations of the moment
> 'automatically', always within what your (super)cell allows. The
> Stoner criterium applied to a paramagnetic DOS might give information
> too.
>
>>      If the calculated result shows that the system
>> have magnetic
>>  moment,
>> must the material be FM? Do the material have the
>> possibility of PM ?
>
> Sure it can be paramagnetic, it all depends on the total energy. It
> can be AF as well... A truly paramagnetic state cannot be calculated
> in wien2k, and is approximated by a 'non-magnetic state' (which
> Gerhard Fecher called a non-word once in this list).
>
> Stefaan
>
>
> Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>
>



-- 
Stefaan Cottenier
Instituut voor Kern- en Stralingsfysica
K.U.Leuven
Celestijnenlaan 200 D
B-3001 Leuven (Belgium)

tel: + 32 16 32 71 45
fax: + 32 16 32 79 85
e-mail: stefaan.cottenier at fys.kuleuven.be


Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm