[Pw_forum] vc-relax & cell_dofree

[Thomas Brumme]

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, SPECBat. 771
> 91191 Gif sur Yvette Cedex, FRANCE
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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> email: cyrille.barreteau at cea.fr
> Web: http://iramis.cea.fr/Pisp/cyrille.barreteau/
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-- 
Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig

Tel:  +49 (0)341 97 36456

email: thomas.brumme at uni-leipzig.de

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