[Pw_forum] honeycomb

[Stefano de Gironcoli]

Aritz Leonardo wrote:

>Hello all:
>
>I am trying to define a honeycomb structure (graphite) but I don't know
>how.
>
>ibrav=?
>  
>
  ibrav =4  (hexagonal lattice )

>which are the lattice vectors?
>  
>
  celldm(1) = a
  celldm(3) = c/a

>and atomic positions?
>
ATOMIC_POSITIONS crystal
C 0.000000000 0.000000000000  0
C 0.333333333 0.666666666666  0
a second layer is placed at z_crystal = 0.5 but I don't know exactly the 
relative shift wrt to the xy origin


>
>thanks
>
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