[Wien] I want to calculate FeNi with lower symmetry

[Peter Blaha]

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)
> 
> 
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> 


                                      P.Blaha
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Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-1-58801-15671             FAX: +43-1-58801-15698
Email: blaha at theochem.tuwien.ac.at    WWW: http://info.tuwien.ac.at/theochem/
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