[QE-users] PbTiO3 slab in vacuum with assume_isolated='2D'

[Lorenzo Paulatto]

Hello Lucian,

is the slab in the center of the cell, or around z=0 ?

Anyway, the option assume_isolated='2D' modifies the Hartree 
interaction, adding a cut-off smooth step function at half the cell 
z-length, i.e. 1/r → step(z)/r. If a long-range 1/r^n propagates outward 
from your slab, at half the cell distance you will see the step 
function. As long as this happens in a region where there is vacuum, it 
is not a problem.

kind regards

On 24/06/2024 13:09, Lucian D. Filip wrote:
>
> Hello,
>
> I am looking at a PbTiO3 slab in vacuum. The slab is in a polarized 
> state and I am trying to obtain the Hartree potential with the dipole 
> correction applied. I have seen that the assumed_isolated = '2D' 
> option should do just that. However, I do not understand the result I 
> am getting. In the attached picture I have plotted the Hartree 
> potential averaged along the z axis, for the polarized state and the 
> centro-simmetric state with polarization zero.
>
> The slab is 5 PTO unit cells thick and there are 20 Angstroms of 
> vacuum on each side. The vacuum region is well above the requirements 
> of assume_isolated ='2D'. Can anyone explain two things:
>
> 1) why are there two regions in vacuum looking like a staircase.
>
> 2) why is there an electric field still present?
>
>
> The weird artefacts at the edges of the supercell are due to the 
> averaging procedure (i am still working on it, not sure where it is 
> coming from).
>
>
> Best regards,
>
> Lucian
>
>
> -- 
> Dr. Lucian Dragos Filip
> National Institute of Materials Physics
> Atomistilor str. 405A, PO Box MG. 7
> Magurele, 077125
> Bucharest, Romania
> E-mail:lucian.filip at infim.ro
> Website:https://lucianfilip.wordpress.com/
>
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-- 
Dr. Lorenzo Paulatto
IdR @ IMPMC - CNRS UMR 7590 & Sorbonne Université
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