[Pw_forum] vc-relax with atomic position fixed.

[Gerardo Ballabio]

On Wed, 2004-05-12 at 09:23, Stefano de Gironcoli wrote:
> with the variable cell relaxation option you can look for combined 
> relaxation of atomic positions and cell at a fixed pressure (not 
> volume... the two things are of course related)
> 
> If the positions are already correct (for symmetry reasons) then the 
> internal forces acting on them should vanish and they will not 
> participate in the relaxation.

You may specify a constraint on the atomic structure, which in this case
is "all atoms are kept fixed". However I'm not sure that this is
possible with variable cell relaxation -- in particular, I wonder
whether atoms would be kept fixed in lattice coordinates (that would be
correct) or in absolute coordinates (that would be wrong).

Gerardo