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

[Peter Blaha]

The YCo5 case is different. Here you may have a hexagonal lattice
(gamma 120degree) or an orthorhombic one (all angles still 90) and
in such a case it is not possible to construct "equivalent" k-meshes,
since the unitcell shape has changed.

If the unitcell shape remains the same, only the symmetry operations
change, than there should be NO such problems. On can choose the same
"total number of k-points in cell", and symmetry will reduce this to two
different (but exactly equivalent) sets of "irreducible k-points.
However, if the unitcell changes, this is not possible.
You can try to do all calculations with the same unitcell (sometimes
possible, maybe sometimes not), or you have to "converge" the k-mesh for
each individual case.

In any case, I doubt that you can get a good value for such a small MAE
(lt. 1 mRy) with just 1000 k-points, but must use many more (test).

In addition, please remember that E-tot will depend crucially on the E-window
(E-max) defined in case.in1 and that you should increase it drastically from
the default 1.5 (and test it!)

> 
> Dear Torsten Andersen, P. Blaha, and Ciao Gerhard,
> 
> 
> Please allow me to explain my purpose in detail.
> 
> 
> I want to calculate MAE of ternary ordered alloy for example FeNi,
> But I can not converge MAE, and MAE varies with parameter changing for
> example R*Kmax.
> 
> 
> For example, my calculation of Fe(Ni)Pt2 is as follows.
> 
> coordinate of Fe(Ni)Pt2 (two times supercell of FePt)  is
> 
> a = 2.72236
> b = 5.44472
> c = 3.66
> Fe(0.0, 0.0, 0.0,), Ni(0.0, 0.5, 0.0), Pt(0.50, 0.25, 0.50), Pt(0.50, 0.75,
> 0.50)
> 
> Parameter of Fe(Ni)Pt2 is
> 
> k =1000
> Emax =10.0
> Gmax =14.0
> Rmt(Fe)=Rmt(Ni)=Rmt(Pt)=2.50
> 
> if I choose R*Kmax = 8.75 MAE is 0.61mRy.
> if I choose R*Kmax = 9.00 MAE is 0.07mRy.
> 
> MAE is calculated as follows.
> MAE = Total energy of hard axis - Total energy of easy axis.
> 
> So MAE is so different with parameter R*Kmax.
> 
> 
> But I found a paper as follows.
> 
> 
> JAP 93, 6888(2003)
> JMMM 264, 7-13(2003)
> PRB 67, 214405(2003)
> PRB 69, 012404(2004)
> PRB 69, 134408(2004)
> 
> 
> They calculate MAE using WIEN2k and they converged MAE. And They say they
> have to unify the symmetry of
> easy axis and hard axis of solid. They calculate YCo5(JMMM 264,
> 7-13(2003)), which symmetry of easy axis is
> P6/mmm, and that of hard axis is Pmmm. And if they do not Pmmm in
> calculation of easy axis , 1 - 5meV error
> happen which is Wien2k's systematical error.
> 
> 
> Is this right ?
> So I want to know total energy dependence of symmetry.
> 
> 
> Best Regards.
> Yasuharu Shiraishi
> 
> 
> 
> 
> 
> 
> 
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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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