[Pw_forum] vc-relax & cell_dofree

[BARRETEAU Cyrille]

Dear QE community

I have a question related to vc-relax and the option cell_dofree.
I want to relax a 2D metal-organic framework (MOF) with hexagonal lattice (ibrav=4)
Could you please explain what is the difference between cell-dofree=xy and cell_dofree=2Dxy?

I have noticed that when using cell_dofree=2Dxy the final CELL_PARAMETER is no longer perfectly hexagonal (see below). Should I use cell_dofree=xy instead and why?

final:
CELL_PARAMETERS (alat= 25.44640422)
   0.990921488  -0.000187347   0.000000000
  -0.495622997   0.858299558   0.000000000
   0.000000000   0.000000000   0.742630080

Thanks in advance

Cyrille

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Cyrille Barreteau
CEA Saclay, IRAMIS, SPEC Bat. 771
91191 Gif sur Yvette Cedex, FRANCE
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+33 1 69 08 38 56 /+33  6 47 53 66 52  (mobile)
email:     cyrille.barreteau at cea.fr
Web:     http://iramis.cea.fr/Pisp/cyrille.barreteau/
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