[Wien] unit in optimization results

[RK_Thapa]

Dear Dr. Miao,
I had also noted this and posted a querry on 28th Sept. If you divide the
volume of the unit cell you get (by optimization)  by 2 (for bcc) and 4 (for
fcc), one get the lattice constant almost equal to the experimental
value.Otherwise, there is a difference of almost 50 % with the experimental
value of a0.
Regards,
R.K.Thapa
==============
Shu Miao wrote:

> Dear Wien2k users
> I'm reporting a problem in the optimization results. The optimize program
> in the new version will automatically fit the optimization results to find
> out the equilibrium volume. According to previous posts in the mailing
> list, this should be the volume in bohr^3 and the lattice parameter of a
> cubic cell can be obtained by taking the cubic root. However, this seems
> not true. I tried with MgO, a cubic material with space group Fm-3m. The
> a0 is about 7.988 bohr. The optimized volume (V0) is 130.1788. This gives
> a cubic root 5.068 bohr. This is far from what it should be. But this is
> not wrong. I find out that the V0 is not the volume of the unit cell, but
> just the volume of a pair of Mg/O. Since this is a FCC structure, it
> contains 4 pairs of Mg/O. If we multiply 130.1788 by a factor 4, the cubic
> root will give correct lattice parameter.
> Has anyone noted this problem? Is it also true for other systems? If so,
> it can be a lot of trouble to get the optimized lattice parameters in a
> low symmetry, multi-atom structure.
>
> Thanks
>
> Shu Miao
> _______________________________________________
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> Wien at zeus.theochem.tuwien.ac.at
> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
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