[QE-users] Dipole correction: should there be a "dip" in the electrostatic potential?

[Thomas Brumme]

Dear Christoph,

which version of QE are you using? Was it compiled with the old XML 
format or the new one?
The new XML format had a bug in the way the input related to the dipole 
correction was saved.
This was solved about a month ago:

https://gitlab.com/QEF/q-e/commit/81a946e15b80972f629c88e47e2545596350f31c

see also the related issue (closed)

https://gitlab.com/QEF/q-e/issues/5

Maybe your problem is due to this. If you use 6.2.1 either download the 
develop branch or
compile using the old XML implementation.

Regards

Thomas

On 18.05.2018 12:50, Christoph Wolf wrote:
> Dear all,
>
> I am (again...) fighting with the dipole correction. I have a system 
> consisting of Ag and MgO centered in the cell around z=0.5
>
> ATOMIC_POSITIONS (crystal)
> Ag       0.000000000   0.000000000   0.323271580
> Ag       0.000000000   0.500000000   0.385512833
> ....
> Mg      -0.000000000   0.000000000   0.721978968
> O        0.500000000   0.000000000   0.723372273
> O       -0.000000000   0.500000000   0.723371161
> Mg       0.500000000   0.500000000   0.721975961
>
> Then I apply tefield and dipfield with
>
>   eamp        = 0.00
>   edir        = 3
>   emaxpos     = 0.95
>   eopreg      = 0.10
>
> which means my system has no discontinuity anywhere in the slab and 
> the field is "physical" between 0.95+0.1-1=0.05 and 0.95 of the z 
> direction.
>
> The SCF cycle converges but the pot_num=11 never becomes horizontal, 
> rather it has a very small slope. I tried to increase the dipole 
> length to see if that makes a difference but apparently it does not 
> help either. With above input the potential amplitude at scf 
> convergence is
>
>      Adding external electric field
>
>      Computed dipole along edir(3) :
>         Elec. dipole          0.4894 Ry au,          1.2440 Debye
>         Ion. dipole           0.4902 Ry au,          1.2460 Debye
>         Dipole                0.2274 Ry au,          0.5779 Debye
>         Dipole field          0.0008 Ry au,
>
>         Potential amp.       -0.0855 Ry
>         Total length         55.5874 bohr
>
>
> Is there a scenario where the dipole correction could fail if the 
> potential is "almost flat" in the vacuum region? If I run the same 
> with VASP I get a small "jump" in the potential making it flat in the 
> vacuum region, so I was wondering why this does not happen (probably 
> different approach in PWSCF)?
>
> Input and resulting potential is attached - any help is welcome!
>
> Thanks in advance and with best wishes,
> Chris
> -- 
> Postdoctoral Researcher
> Center for Quantum Nanoscience, Institute for Basic Science
> Ewha Womans University, Seoul, South Korea
>
>
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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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