[QE-users] Tetragonal vc-relax, is breaking the symmetry

[Lucas Nicolás Lodeiro Moraga]

Hi all !

I am performing a vc-relax calculation over tetragonal crystal, for that a
put: ibrav=6 ; celldm(1)=16.64 ; celldm(3)=1.44 ; cell_dofree= xyz.

I believed if i was doing the vc-relax with these parameters, the
calculation would keep fixed a=b, and the tetragonal symmetry remains. But
the results show that the first and second cell parameters are not equals
(they remains orthogonal). Before that i tried it using different types of
ibrav and different methods for cell_dofree, but in all cases  the
tetragonal symmetry breaks.

I have read in others forums that the symmetries operations remains fixed
in the calculation... but in my case the crystal it is very complex, and
the calculation show in the beginning: No symmetry found. I think that this
is why the calculation "breaks the tetragonal symmetry", because it does
not found any symmetry operation... and the cell vectors symmetry is not
attended. Is what i say okay?

There are other methods to do this, that maintain the relation a=b fixed?

I have thought a iterative method for vc-relax to maintain the tetragonal
relation, but it would take a lot of time, and i do not know if it give a
correct result.

Sorry if this is a too basic question, but i have searched the
documentation and could not find it (or maybe i could not understand it
well). Any tips will be greatly appreciated.

Best regards
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