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[c.gross@physik.uni-frankfurt.de]

Hello everybody,

this is (probably) a newbie question...

I am trying to define the unit cell of MgZn2 (primitive hexagonal) by the 
following lines in my input file:

------------

#Definition of the unit cell
acell 5.223 5.223 8.5666 angstrom
angdeg 90 90 120     # hexagonal cell
spgroup 194          # space group no 194, P63/mmc

#Definition of the atom types
ntypat 2             # Two types of atoms (Mg, Zn)
znucl 12 30          # The keyword "znucl" refers...
                         
#Definition of the atoms
natom 3              # There are three atoms
typat 1 2 2          # First atom: type 1, second: type 2, third: type 2
xred                 # This keyword indicate that the location of the atoms
                     # will follow, one triplet of number for each atom
1/3 2/3 0.06286      # Triplet giving the REDUCED coordinate of atom 1 (Mg).
0.83048 0.66096 1/4  # Triplet giving the REDUCED coordinate of atom 2 (Zn2).
0 0 0                # Triplet giving the REDUCED coordinate of atom 3 (Zn1). 

(...)
------------

But, ABINIT sends lots of warnings of the following type to the log file (and 
finally stops):

------------

 symatm : WARNING -
  Trouble finding symmetrically equivalent atoms
  Applying inv of symm number  2 to atom number   1  of typat  1
  gives tratom=  6.6667E-01  3.3333E-01 -4.3714E-01.
  This is further away from every atom in crystal than the allowed tolerance.
  The inverse symmetry matrix is  0 -1  0
                                  1  1  0
                                  0  0  1
  and the nonsymmorphic transl. tnons =    0.0000000    0.0000000    0.5000000
  The nearest coordinate differs by  3.333E-01 -3.333E-01  5.000E-01
  for indsym(nearest atom)=    1

  This indicates that when symatm attempts to find atoms symmetrically
  related to a given atom, the nearest candidate is further away than some
  tolerance.  Should check atomic coordinates and symmetry group input data.

------------

Is this a problem with my input file ? Am I using the SPGROUP command 
correctly, or am I supposed to provide the positions of all atoms in the unit 
cell, not just the asymmetric unit ?

I would be thankful for a hint,
Christoph