[Wien] diff. between triclinic and hexagonal

[Peter Blaha]

> I have difficulties to define a hexagonal unit cell with a number of atoms.
>
> nn and sgroup reduce my symmetry to P1 and triclinic, even though my unit cell is of the type a,a,c and gamma=120? These lattice settings are not changed by sgroup and nn. So I end up with a "triclinic" unit cell, with hexagonal lattice parameters? Is this a Wien convention issue?

Even when you use a "cubic unit cell" (a=b=c, angles=90), but you put one
single atom at (0,0,0) and another one at (x,y,z), what comes out is NOT
cubic. Eventually there will be ONLY the identity left as symmetry operation
and then this is called P1.

The symmetry of the unit cell alone does NOT determine the spacegroup.

                                      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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