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[Andrey Chibisov <andreichibisov@yandex.ru>]

Can you help me with unit cell of Cristobalite?
Data for Cristobalite from site http://rruff.geo.arizona.edu/AMS/amcsd.php 
(American Mineralogist Crystal Structure Database) is:

Title               Cristobalite
Lattice type        F
Space group name    Fd-3m
Space group number  227
Setting number      1

Lattice parameters
   a        b        c       alpha    beta     gamma
 7.16600  7.16600  7.16600  90.0000  90.0000  90.0000
Unit-cell volume = 367.985229
Structure parameters
                       x          y          z          g          B
   1 Si  Si          0.12500    0.12500    0.12500    1.000    3.335
   2 O   O           0.00000    0.00000    0.00000    1.000    7.146

In the input abinit file I write:
spgroup 227
For the primitive vectors of the lattice form a FCC lattice:
  rprim 
        0.0 0.5 0.5
        0.5 0.0 0.5
        0.5 0.5 0.0
However the abinit gives out:
Unit cell is not primitive?
In what is my error?
     
-- 
Andrey Chibisov.
Candidate of Science,
Structural Ceramics Laboratory
Institute of Geology and Nature Management 
Far Eastern Branch of Russian Academy of Sciences