AW: [Wien] I want to calculate FeNi with lower symmetry

[Gerhard Fecher]

Is there a confusion about symmetry ?

The symmetry of the atom positions is independent of the magnetisation if you do not have magnetostriction.

If you consider the spin or a magnetization, you have to remove some more symmetry operations, as (for example) every vertical mirror operation will change the sign of the spin.
For bcc-Fe with the atomic positions in I m-3m you will have the color groups (group in brackets transforms the spin correctly)
for B || 001  I 4/mmm (I 4/m) (you see 2 mirror m's are removed, only the h one remained)
for B || 110  F mmm (C 2/n)
for B || 111  R -3m  (R -3)  

Please, consult e.g.: Koster, Dimmok, Wheeler and Satz; properties of the thirty-two point groups to see what may apply for youre FeNi case.

Ciao Gerhard

-----Ursprüngliche Nachricht-----
Von: wien-bounces at zeus.theochem.tuwien.ac.at im Auftrag von Peter Blaha
Gesendet: Mi 30.11.2005 08:11
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] I want to calculate FeNi with lower symmetry
 
FeNi seems to be a "binary" alloy!

Usually this has even cubic symmetry!, but as you specified in a second 
posting, you added spin-orbit coupling and this changes symmetry from 
cubic to tetragonal (P4/mmm).

When you want to run this in "orthorombic symmetry (Pmmm) the 
simplest way is to change a,b,c lattice parameters slightly during 
init_lapw. This will of course lead to the desired orthorhombic symmetry. 
After initialization, don't forget to change the lattice parameters back 
to their original value.

When you do everything right, however, the symmetry MUST NOT change the 
total energy !
A lower symmetry will lead to a larger k-mesh (eg. the (100) and (010) 
k-points will both be in your set (and will have identical eigenvalues),
while in the tetragonal symmetry only (100) is used, 
so you simply need more cpu time without gaining anything.

In some cases you may even run into troubles, since EF could coincide with 
a state at such degenerate k-points, leading to possible instabilities in 
the scf cycle.

In essence: There is not much reason to lower symmetry in your case.  

>   I want to calculate ternary ordered alloy FeNi with lower symmetry.
> 
>   Wien2k's command "symmetry" judge FeNi's symmetry as P4/mmm.
>   But  I  want  to set FeNi's symmetry as Pmmm which is lower symmetry than
>   P4/mmm.
>   How can I do it ?  Do I have to set this by hand?
> 
>   Best Regards.
> 
>   Coordinate of FeNi is as follows.
>   Fe(0.0, 0.0, 0.0)
>   Ni(0.5, 0.5, 0.5)
> 
> 
> _______________________________________________
> Wien mailing list
> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> 


                                      P.Blaha
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