I have a problem to build the correct structure  of graphene.

I use these parameter

space group of graphene is 191

lattice constant is a=b=2.46A , c=6.71 A

The position of the two atom basis are

C1 (0.000  0.00  0.00)

C2 (0.00  0.577350269  0.00)

but i cannot get the right structure of graphene

Every time it give me this error  chosen position is within the specified tolerance  (1.0 A) of a symmetry copy of itself.

Best regards

Omar