[QE-users] dipfield

[Thomas Brumme]

Dear Asad,

please also answer to the list ;) ("reply all")

No! It's either dipfield = .true. or assume_isolated ='2d'. If you want 
to simulate "a real" 2D system using
the Coulomb cutoff you don't need to correct due to the systems dipole. 
And if you correct with the artificial
dipole, cutting of the Coulomb will result in something bad/weird... 
Actually, I don't know if this will work at all.

So, either dipfield = .true. or assume_isolated ='2d'

Thomas


On 11/13/18 11:45, Asad Mahmood wrote:
> Thanks Thomas for reply. So I need to include both flags(i.e dipfielf 
> = .true and assume_isolated ='2d' ) in relax or structure optimization 
> calcations ?
>
> On Tue, Nov 13, 2018, 3:11 PM Thomas Brumme 
> <thomas.brumme at uni-leipzig.de <mailto:thomas.brumme at uni-leipzig.de> wrote:
>
>     Dear Asad,
>
>     What is the benefit of using dipfield=.true.? Well, the benefit is
>     that you get the correct electronic structure,
>     energetics, and so on. As you want to simulate a 2D system with 3D
>     boundary conditions this is the only
>     correct way if you have an asymmetric system (in the z-direction,
>     assuming the 2D system is in xy). Well,
>     not the only correct way. Recently a Coulomb cutoff technique was
>     implemented in QE, check input flag
>     assume_isolated='2D'
>
>     Regards
>
>     Thomas
>
>     P.S.: If you have a dipole in your system you'll see that
>     properties (especially the total energy) will change
>     with increasing vacuum region. If you increase it, you'll minimize
>     the eigenfunction overlap between the
>     repeated layers but the Coulomb interaction will never be zero and
>     thus you can get wrong results - and
>     this will be worse for larger dipole, e.g., the flourinated graphene.
>
>     On 11/13/18 08:38, Asad Mahmood wrote:
>>     Hi,
>>
>>     I have a hexagonal graphene(or any other) monolayer and I
>>     hydrogenate(or flourinate, etc.) on the top surface only (single
>>     sided). Is there need to use flag dipfield = .true ? What is
>>     benefit or disadvantage of using this flag for optimization of
>>     L.C or bond length?
>>     I am using 20 angstrom vacuum between two layers to avoid mutual
>>     influence.
>>
>>
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>
>     -- 
>     Dr. rer. nat. Thomas Brumme
>     Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
>     Leipzig University
>     Phillipp-Rosenthal-Strasse 31
>     04103 Leipzig
>
>     Tel:  +49 (0)341 97 36456
>
>     email:thomas.brumme at uni-leipzig.de <mailto:thomas.brumme at uni-leipzig.de>
>

-- 
Dr. rer. nat. Thomas Brumme
Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry
Leipzig University
Phillipp-Rosenthal-Strasse 31
04103 Leipzig

Tel:  +49 (0)341 97 36456

email: thomas.brumme at uni-leipzig.de

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