[Pw_forum] Vacuum for non-periodic structure

[Anik Mondol]

Thank you a lot , David Foster, Giovanni Cantele. Appreciate your response

Anik Kumar Mondol
Bangladesh University of Engineering and Technology

On Wed, Nov 29, 2017 at 3:30 PM, Giovanni Cantele <
giovanni.cantele at spin.cnr.it> wrote:

> Hi, if you want to study a nanowire, I do not see the reason why to
> optimise the unit cell along x and y directions.
> Either freeze these two degrees of freedom in vc-relax or, much simpler,
> change c parameter (lattice parameter along the z direction)
> and evaluate E(c) (total energy as a function of c). A parabolic fit will
> help you in finding the lowest energy configuration.
>
> Generally speaking, to establish whether the vacuum is enough, calculate
> in at least one case the property you are interested in for two different
> values of the vacuum and see if any appreciable change is observed.
> Another check is that the band structure should be flat (no dispersion)
> along x and y
>
> Giovanni
>
>
>
> On 29 Nov 2017, at 06:28, Anik Mondol <anikmondol1206 at gmail.com> wrote:
>
> Dear Users,
> I am doing a DFT calculation of GaN nanowires, While designing the
> nanowire (approximately 10 A diameter) , I had added around 10 A of vacuum
> on x and y direction. Now I have performed a vc-relax calculation before
> band calculation, the cell volume has shrunk . The vacuum has decreased .
> Now to make sure the results don't be affected by the identical replicas ,
> at least  how much vacuum is needed ? Now, that the vacuum has shrunk, will
> that impose any effect on results in this respects. I mean, How can I be
> sure this vacuum is enough?
>
> Mondol Anik Kumar
> Bangladesh University of Engineering and Technology
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> --
>
> Giovanni Cantele, PhD
> CNR-SPIN
> c/o Dipartimento di Fisica
> Universita' di Napoli "Federico II"
> Complesso Universitario M. S. Angelo - Ed. 6
> Via Cintia, I-80126, Napoli, Italy
> e-mail: giovanni.cantele at spin.cnr.it <giovanni.cantele at spin.cnr.it>
> Phone: +39 081 676910 <+39%20081%20676910>
> Skype contact: giocan74
>
> ResearcherID: http://www.researcherid.com/rid/A-1951-2009
> Web page: http://people.fisica.unina.it/~cantele
>
>
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