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

[Christoph Wolf]

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
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