AW: AW: [Wien] magnetic calculation

[Gerhard Fecher]

I agree completely with Stefaan,
Ab-initio programs are not black boxes where one puts in atoms and a crystal structure with physical properties comes out.

I had similar questions from one of my students some time ago, so this contribution reminded me about that. Now, I asked some students to try whether they can find the "correct" ground states of Cr, (Mn), Fe, Co, and Ni. Mn is in () as its structure may be too complicated for a practice. I doubt it works, however, I hope those students are afterwards perfect in operating Wien2k.

Ciao
Gerhard


-----Ursprüngliche Nachricht-----
Von: wien-bounces at zeus.theochem.tuwien.ac.at im Auftrag von Stefaan Cottenier
Gesendet: Do 08.12.2005 13:27
An: A Mailing list for WIEN2k users
Betreff: Re: AW: [Wien] magnetic calculation
 
Aditionnaly, it is sometimes necessary to take also the geometry of the 
unit cell into account. At a fixed set of lattice constants, a 
ferromagnetic solution might have a lower energy than a nonmagnetic one, 
but at another set of lattice constants it might be different. Finding 
the correct predicition for the ground state can be a lot of work... 
(and then I don't even mention high-spin/low-spin ferromagnetic 
solutions that might both exist, possible noncollinear magnetism, more 
complex arrangements than just simple antiferromagnetic,.... -- in 
principle all of them have to be tried, and all of them as a function of 
unit cell geometry).

Stefaan

>This depends a little bit, I think a spin polarized calculation for Al will result always in a non ferromagnetic state. Its different if you go e.g. to 3d metalls were you may have a ferromagnetic result for Cr even Cr is not a ferromagnet. 
>In some cases you do not find an anti-ferromagnetic groundstate if you start with a ferromagnetic alignment of the spins, there you may have to change the spin of some atoms (depending on the complexity of the problem) such that the scf will find the lower energy for the AFM state. For compunds I try usually all possibilities and then compare the total energies. (Check that the charge convergence is ok and not only the energy and don't use too small numbers of k-points, in ferro- ferri- or af magnetic cases you can check for example fast whether the increase of k-points causes large shifts of Ef or the moments in the case.scfm file.)
>
>Actually, I prefer to do the experiment first and then check with the calculation, but thats a matter of taste and capabilities.
>
>Ciao
>Gerhard
>
>-----Ursprüngliche Nachricht-----
>Von: wien-bounces at zeus.theochem.tuwien.ac.at im Auftrag von li wf
>Gesendet: Do 08.12.2005 12:23
>An: wien at zeus.theochem.tuwien.ac.at
>Betreff: [Wien] magnetic calculation
> 
>Dear wien users,
>
>     i want to calculate the electronic structure and magnetism of a 
>compounds whose magnetism is still unknown. i have a puzzle that if i take 
>a spin polarized calculation and found that it is spin-polarized, can i say 
>that this compounds is ferromagnetism? should i also take 
>antiferromagnetism calculation and them compare the total energy of the 
>two? if a compound is not ferromagnetism, will the spin polarized 
>calculation always give a non-magnetism result?
>
>    thank you very much.
>
>    best regards,
>
>   wane
>
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