[Pw_forum] vc-relax & cell_dofree

[BARRETEAU Cyrille]

Thanks for your reply but I am still not very sure I understand well the difference between the two options:
'xy' :     only v1_x and v2_y are moved
'2Dxy' :     only x and y components are allowed to change

When the vectors v1 and v2 are not orthogonal (which is my case) the option 'xy' is not appropriate ?

Cyrille

========================
Cyrille Barreteau
CEA Saclay, IRAMIS, SPEC Bat. 771
91191 Gif sur Yvette Cedex, FRANCE
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+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/
========================
________________________________
De : pw_forum-bounces at pwscf.org [pw_forum-bounces at pwscf.org] de la part de Thomas Brumme [thomas.brumme at uni-leipzig.de]
Envoyé : mardi 25 juillet 2017 11:32
À : pw_forum at pwscf.org
Objet : Re: [Pw_forum] vc-relax & cell_dofree


Dear Cyrille,


from the input description:

'xy' :     only v1_x and v2_y are moved

'2Dxy' :     only x and y components are allowed to change

Thus, even in the case of cell_dofree='xy' I think the cell will change. Anyway, the deviation from 120 DEG is quite small (119.43 DEG if I'm not wrong) - I don't know if this could be do to numerical issues. Maybe try starting a new relaxation with a hexagonal cell but smaller in-plane lattice vector of ~99.1%


Cheerio


Thomas

On 07/25/17 09:08, BARRETEAU Cyrille wrote:
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

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