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

[Lucian D. Filip]

I also tried centering the slab around z=0 and now I am even more 
confused. In the attached picture, the Hartree potential has basically 
changed sign. What is the proper way to use the assume_isolated=2D method?

Best regards,

Lucian

On 25-Jun-24 8:14 AM, Lorenzo Paulatto wrote:
>
> 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
> phone: +33 (0)1 442 79822 / skype: paulatz
> http://www.impmc.upmc.fr/~paulatto/ - https://anharmonic.github.io/
> 23-24/423 B115, 4 place Jussieu 75252 Paris CX 05
>
> _______________________________________________
> The Quantum ESPRESSO community stands by the Ukrainian
> people and expresses its concerns about the devastating
> effects that the Russian military offensive has on their
> country and on the free and peaceful scientific, cultural,
> and economic cooperation amongst peoples
> _______________________________________________
> Quantum ESPRESSO is supported by MaX (www.max-centre.eu)
> users mailing listusers at lists.quantum-espresso.org
> https://lists.quantum-espresso.org/mailman/listinfo/users

-- 
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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