[QE-users] dipfield

[Thomas Brumme]

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

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