[Wien] magnetism calculation in Wien2K

[villesuzanne]

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


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