[Wien] x symmetry problem

[Peter Blaha]

> Sorry, I would just like to clarify this for myself. When you refer to a
> 'doubled P cell', do you mean that as the asymmetric unit of the
> primitive cell is twice that of the higher symmetry centered cell, you
> have to double the asymmetric unit size (rather than the entire cell)?
> And when you refer to a 'triclinic P cell of the same size', this is
> referring to a cell the same size as the monclinic centered cell?

What I mean with that is (this im my "recipie" how I do it):
Once you have the proper structfile corresponding to the B... spacegroup
(you should see a "lattice"=CXZ type in vi case.struct)
you change the "Lattice type" into P
Then you double the number of atoms (lets assume you had 3 independent
positions, now you get 6) and "duplicate" the whole block of atoms (in
your favorite editor). Now you add to each of those new positions (0.5,0,0.5)
(make sure the values are between 0 and 1!!!).
"Label" the new atoms by changing eg. "Ni" to "Ni1", so that WIEN does
not reduce them to a smaller cell.

Alternatively (I've never done this) you could construct a triclinic cell,
which could keep the number of atoms the same. However, you would have to
calculate the triclinic angles yourself and in particular you have
to convert the positions to fractions of the new basisvectors.

> Basically, I am wondering if it is sufficient to lower the symmetry from
> C112/m (for example) to the subgroup P112/m? This would have the same
> size of unit cell (twice the size of asymmetric unit), and unique axis
> c.
Probably, but I'm not so familiar with spacegroup symmetries that I can say
yes.

                                      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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