[Pw_forum] relax or vc-relax for supercell?

[yavar pour azar]

Dear QE users,

I want to  build * *the supercell.
primarily, I do vc-relax calculation on the bulk structure. (until force
and pressure ~0)
in the next step, I build the supercell by bulk ideal atomic positions,
and finally I should use relaxation.
in this level,  the vc-relax is necessary or just the relax?

when I used only the relax'  option, after relaxation of  supercell
pressure was about 10Kbar, is this means that I should use vc-relax.

If this is true, what is physical interpretation of changes in lattice
parameters? this means outermost layer's cell differ from interior ones?


thanks in advance.

Yavar  Taghipour
PhD student

Physics Group.AEOI. Tehran. Iran
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