[Pw_forum] vc-relax & cell_dofree

[Paolo Giannozzi]

It is easier to figure out what the various "cell_dofree" options do from
the code than from the documentation: look for routine 'init_dofree" in
Modules/cell_base.f90 (iforceh(i,j)=0 means "keep component i of basis
vector j fixed")

Paolo

On Tue, Jul 25, 2017 at 12:19 PM, BARRETEAU Cyrille <
cyrille.barreteau at cea.fr> wrote:

> 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%201%2069%2008%2038%2056> /+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
> 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 <+49%20341%209736456>
>
> email: thomas.brumme at uni-leipzig.de
>
>
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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