[QE-users] dipfield

[Dr. Thomas Brumme]

Both methods should give the same result - they did at least when I  
tried. But you can't calculate phonons with dipole correction so if  
you want those start with assume_isolated = '2D'
But read all infos given in input_pw and the related papers - it helps  
to understand how to setup the system ;)

Thomas

Zitat von Asad Mahmood <amahmood at phys.qau.edu.pk>:

> Thank you Thomas, I will try both flag one by one and see what change do
> each of them brings separately.
>
> On Tue, Nov 13, 2018 at 3:52 PM Thomas Brumme <thomas.brumme at uni-leipzig.de>
> wrote:
>
>> 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
>> 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
>>>
>>>
>> --
>> 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
>>
>>