[Pw_forum] question on ibrav=0

Lorenzo Paulatto paulatto at sissa.it
Fri Dec 7 16:26:19 CET 2007

On Fri, December 7, 2007 16:13, Guoying Gao wrote:
> Dear everyone,
>     I read the manual of QE and find that for ibrav=0, the
> CELL_PARAMETERS has two choices.
> one is cubic and the other is hexagonal. So I want to know in which
> case we use cubic and  in which
> one the other.

Dear Guoying Gao,
I'm just copying and pasting from Doc/INPUT_PW, but I think this is what
you wanted to know:


  optional card, needed only if ibrav = 0 is specified, ignored otherwise


    CELL_PARAMETERS { cubic | hexagonal }
      a(1,1) a(2,1) a(3,1)
      a(1,2) a(2,2) a(3,2)
      a(1,3) a(2,3) a(3,3)

  a(:,1) = crystal axis 1    alat units   if celldm(1) was specified
      2                 2    a.u.         if celldm(1)=0
      3                 3
  Keyword "cubic" or "hexagonal" specify if you want to look for symmetries
  derived from the cubic symmetry group (default) or from the hexagonal
  symmetry group (assuming c axis as the z axis, a axis along the x axis)

Lorenzo Paulatto
+39 040 3787 511

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