[Wien] showing rhombohedral in hexagonal symmetry

[Stefaan Cottenier]

> I want to make a struct file for a rhombohedral compound but with
> hexagonal symmetry. How can i do that?
> the positions in rhomboherdral are (0 0 0) (2/9 2/9 2/9) (7/9 7/9 7/9)
> with 166-R3m
> the equivalent positions by using rhom2hex are (0 0 0) (0 0 0.22) (0 0
> 0.77) with H space group, with this positions WIEN2K suggest 183 (P 6 m
> m) space group which seems it is not correct because i think in regard
> to crystallography, the number of atom during the conversion from
> rhombohedral to hexagonal may change.

Sure, the number of positions is three times larger in the hexagonal 
setting, but these are symmetry-related.

Sm has 1a and 2c positions occupied in the rhombohedral setting (x=2/9), 
and 3a and 6c in the hexagonal setting (z=2/9). rhomb2hex and hex2rhomb 
make the correct conversions, but the symmetry-related positions have to 
be added manually.

Compare:

http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=166&grha=rhombohedral

http://www.cryst.ehu.es/cgi-bin/cryst/programs/nph-wp-list?gnum=166&grha=hexagonal

(mind the three translations under the word 'coordinates', which bring 
the 2 specified positions to 6)

The case.struct which you search for, is pasted hereafter.

Stefaan


blebleble
H   LATTICE,NONEQUIV.ATOMS   2  166 R-3m
MODE OF CALC=RELA unit=bohr
   6.856115  6.856115 49.573186 90.000000 90.000000120.000000
ATOM  -1: X=0.00000000 Y=0.00000000 Z=0.00000000
           MULT= 3          ISPLIT=15
       -1: X=0.66666667 Y=0.33333333 Z=0.33333333
       -1: X=0.33333333 Y=0.66666667 Z=0.66666667
Sm         NPT=  781  R0=.000010000 RMT=   2.50000   Z:  62.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                      0.0000000 1.0000000 0.0000000
                      0.0000000 0.0000000 1.0000000
ATOM  -2: X=0.00000000 Y=0.00000000 Z=0.22222222
           MULT= 6          ISPLIT=15
       -2: X=0.66666667 Y=0.33333333 Z=0.55555556
       -2: X=0.33333333 Y=0.66666667 Z=0.88888889
       -2: X=0.00000000 Y=0.00000000 Z=0.77777778
       -2: X=0.66666667 Y=0.33333333 Z=0.11111111
       -2: X=0.33333333 Y=0.66666667 Z=0.44444444
Sm         NPT=  781  R0=.000010000 RMT=   2.50000   Z:  62.00000
LOCAL ROT MATRIX:    1.0000000 0.0000000 0.0000000
                      0.0000000 1.0000000 0.0000000
                      0.0000000 0.0000000 1.0000000
    0      NUMBER OF SYMMETRY OPERATIONS