[QE-users] dipole correction - "saggy" electrostatic potential?

[Christoph Wolf]

Dear Thomas,

thank you for your detailed replies which were, as always, very helpful!


Best,
Chris

On Mon, Jul 2, 2018 at 2:57 PM, Dr. Thomas Brumme <
thomas.brumme at uni-leipzig.de> wrote:

> Dear Chris,
>
> adding to my last reply: in the end, it all, of course, depends on what
> you want to simulate. If you're aiming for a charged species on a surface
> then assume_isolated='2D' might be wrong if you don't increase the slab
> (mimicking the surface of a bulk material) such that the electric field
> at the bottom does not influence the top. It might be worth to also look
> at my implementation of a gate setup (gate=.true.) or to wait till the
> author of assume_isolated='2D', Thibault Sohier, releases his
> implementation
> including the gate setup. Gate? Maybe check this paper to see why this
> could be useful:
>
> https://www.sciencedirect.com/science/article/pii/S0169433218315022
>
> As I said, it all depends on the situation you want to simulate. But a
> flat potential with the same absolute value on both sides of the system
> is rarely correct for a charged system.
>
>
> Regards
>
> Thomas
>
> Zitat von Christoph Wolf <wolf.christoph at qns.science>:
>
> Dear Thomas,
>>
>> I played a bit with "assume_isolated='2D'" but I do not think that this
>> can
>> correct the electrostatic potential of charged sytems (in the sense that
>> the potential becomes "flat") unless I am interpreting the output
>> (attached) wrong.
>>
>> One way that gives me a flat vacuum potential is to use the M-P scheme but
>> that only works for cubic systems. After reading about the implementation
>> in VASP a bit I also think that is what they recommend.
>>
>> Best,
>> Chris
>>
>> On Thu, Jun 28, 2018 at 7:04 PM, Dr. Thomas Brumme <
>> thomas.brumme at uni-leipzig.de> wrote:
>>
>> Dear Chris,
>>>
>>> The potential shows the typical quadratic dependence on z since you're
>>> calculating a charged system - there is a homogeneous background charge
>>> since the 3D pbc system is assumed to be neutral. This has nothing to do
>>> with the dipole correction. Depending on what you want to do next it
>>> might
>>> be useful to set the flag assume_isolated='2D'
>>>
>>> Regards
>>>
>>> Thomas
>>>
>>> Zitat von Christoph Wolf <wolf.christoph at qns.science>:
>>>
>>>
>>> Dear all,
>>>
>>>>
>>>> I am still observing something strange in my slab + dipole correction
>>>> calculation that I do not fully understand.
>>>>
>>>> When using dipfield+tefield (eopreg and emaxpos well within the vacuum
>>>> region) I encounter a "saggy" electrostatic potential (plot_num=11)
>>>> despite
>>>> the sawtooth efield potential (plot_num=12) looking as usual. Maybe
>>>> someone
>>>> can give it a look and confirm if this is due to the excess charge in
>>>> the
>>>> system (this does not happen when running the same system in VASP)?
>>>>
>>>> I attach input and the plot of the potential for 2 and 4 layers of
>>>> vacuum
>>>> (more vacuum does seem to improve the situation).
>>>>
>>>> Thank you in advance for your time and assistance!
>>>>
>>>> Chris
>>>>
>>>> PS: I am using a QE version with dipole bug fix:
>>>>
>>>>      Program PWSCF v.6.2.2 starts on 25Jun2018 at 10:39:24
>>>>
>>>> --
>>>> Postdoctoral Researcher
>>>> Center for Quantum Nanoscience, Institute for Basic Science
>>>> Ewha Womans University, Seoul, South Korea
>>>>
>>>>
>>> --
>>> 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
>>>
>>>
>>>
>>
>> --
>> Postdoctoral Researcher
>> Center for Quantum Nanoscience, Institute for Basic Science
>> Ewha Womans University, Seoul, South Korea
>>
>
>
>
>


-- 
Postdoctoral Researcher
Center for Quantum Nanoscience, Institute for Basic Science
Ewha Womans University, Seoul, South Korea
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