[Pw_forum] adding vacuum

[Jaret Qi]

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
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> 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 :
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> /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


  
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