[Wien] How to generate the C19 structure (alpha-Sm)

[Michael Fischer]

Hello,

I think that (0 0 2/9) are coordinates in hexagonal setting. You want 
them in rhombohedral setting, so try transforming them to (2/9 2/9 2/9) 
- this is a special position generating 2 atoms in the rhombohedral 
cell, i.e. 6 atoms in the hexagonal cell. Together with the atom at the 
zero point, this delivers a total of 3 atoms per rhombohedral cell or 9 
atoms per hexagonal cell. Is that the number of atoms that you expect 
per cell?
With this, I get each atom twelve-fold coordinated with an interatomic 
distance of 3 Å when using a = 3 Å and c = 22 Å as approximate values 
for the lattice parameters. I am not too familiar with the type of 
structure you are investigating, but as it is derived from ccp- and 
hcp-structures, I think that this should be ok.

Best regards
Michael