[Pw_forum] adding vacuum

[Pascal Boulet]

So, I think in this case you should also relax the z-axis: The system tends to fill the vacuum by moving atoms since it cannot adapt the cell parameter.

Pascal

Le 16 nov. 2015 à 21:49, Jaret Qi <jaretqi at yahoo.com> a écrit :

> To make it clear, I am not adding vacuum to isolate my system like in graphene where we make the z-axis large enough to make it graphene not graphite. My system is a (001) interface between semi-metallic and semiconductor, so i am trying to minimize the interaction along the interface which is along the z-axis and study some properties and match it with experimental results. I need a reasonable vacuum so I began with 4A.
> 
> 
> 
> 
> 
> On Monday, November 16, 2015 1:31 PM, Nicola Marzari <nicola.marzari at epfl.ch> wrote:
> 
> 
> On 16/11/2015 21:17, Jaret Qi wrote:
> > but that will cost time!
> 
> you are right! just keep the 4 angstroms, no one will notice.
> 
> (actually, skip the calculations altogether, and make up some
> plausible numbers in your paper - that will be even faster).
> 
>             nicola
> 
> >
> >
> >
> > On Monday, November 16, 2015 9:26 AM, Pascal Boulet
> > <pascal.boulet at univ-amu.fr> wrote:
> >
> >
> > Hello,
> >
> > 4 angstroms wide seems to be very small for the vacuum. As a rule of
> > thumb you should use at least 2.5 times the thickness of your slab. This
> > is what we observed in the calculations of semiconductor slabs. This has
> > to be tested.
> >
> > Pascal
> >
> > Le 16 nov. 2015 à 16:40, Jaret Qi <jaretqi at yahoo.com
> > <mailto:jaretqi at yahoo.com>> a écrit :
> >
> >> Hello all,
> >> I am trying to minimize the interaction between my system and its
> >> periodic images. To do so, I introduced a layer of vacuum along the
> >> z-axis by increasing the lattice vector along the z-axis by 4A. At the
> >> same time, I fixed it by using this parameter: cell_dofree='2Dxy',
> >> But I have noticed atoms that are close to the vacuum move along the
> >> z-axis and vacuum is decreasing, is this wrong or I should use
> >> different cell_dofree?
> >> note:relaxation still ongoing, not relaxed yet.
> >>
> >>
> >> JARET,
> >> ASU
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> >
> > --
> > Pascal Boulet /- MCF HDR, Resp. L1 MPCI - DEPARTEMENT CHIMIE/
> > Aix-Marseille Université - ST JEROME - Avenue Escadrille Normandie
> > Niemen - 13013 Marseille
> > Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50
> > Site : http://allos.up.univ-mrs.fr/pascal - Email :
> > pascal.boulet at univ-amu.fr <mailto:pascal.boulet at univ-amu.fr>
> > /Afin de respecter l'environnement, merci de n'imprimer cet email que si
> > nécessaire./
> 
> >
> >
> >
> >
> >
> > _______________________________________________
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> 
> >
> 
> -- 
> ----------------------------------------------------------------------
> Prof Nicola Marzari, Chair of Theory and Simulation of Materials, EPFL
> Director, National Centre for Competence in Research NCCR MARVEL, EPFL
> http://theossrv1.epfl.ch/Main/Contact http://nccr-marvel.ch/en/project
> 
> 
> 

--
Pascal Boulet - MCF HDR, Resp. L1 MPCI - DEPARTEMENT CHIMIE
Aix-Marseille Université - ST JEROME - Avenue Escadrille Normandie Niemen - 13013 Marseille
Tél: +33(0)4 13 55 18 10 - Fax : +33(0)4 13 55 18 50
Site : http://allos.up.univ-mrs.fr/pascal - Email : pascal.boulet at univ-amu.fr
Afin de respecter l'environnement, merci de n'imprimer cet email que si nécessaire.

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