[CP2K-user] [CP2K:13550] IC-QMMM with single charge in front of a metal plane: open boundary corrections

[Dorothea Golze]

Dear Katharina,

in short, it is very likely no bug; I think the basic problem is that you
try to run a periodic DFT calculation for a charged system.
The constant potential condition is a hard constraint for the average. I
tested with the standard periodic solver (for periodic systems) and the MT
solver (for a cluster-type of approach).
I don't have it in the paper, but in my thesis, I have an example, where I
placed an ion above a slab (Figure 3.7 page 31,
https://www.zora.uzh.ch/id/eprint/116638/)
For the MT solver, I have the suspicion you are not applying this solver
correctly, which can lead to technical artifacts. You need lots of vacuum
around your system since you also specified a periodic cell, this seems not
to be the case. I suggest to test the MT solver for a single molecule (DFT
only) first to get a feeling how much vacuum you need, i.e., to converge
out the cell size and how this solver behaves.

Best regards,
Dorothea


Am Fr., 26. Juni 2020 um 16:32 Uhr schrieb Katharina Doblhoff-Dier <
k.doblh... at lic.leidenuniv.nl>:

> Dear Dorothea,
> To break a complex problem down: Should I consider it a bug, that I get
> non-constant potentials in the plot of the hartree energies, when using MT
> or implicit BCs and that potential in the metal does not match
> EXT_POTENTIAL? (see plot below - also posted in the original question) Or
> is there a good reason for this behavior?
>
> red:      IMPLICIT poissn solver with Neumann BC at z=0 and z=60 and
>>> homogeneous Dirichlet BC at z=30
>>> green:  MT (Martyna-Tuckerman) poisson solver (shifted by 0.4V)
>>> blue:    normal Ewald summation (shifted by 0.4V)
>>>
>>> [image: tmp3.png]
>>>
>>>
>>>
>>> Thank you for your help!
> Best regards,
> Katharina
>
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