Ewald and charged simulation box

[Gianni Carifaccia]

Dear All,

I need to simulate a charged QM system (I need to see what happens after
protonation of my molecule) and I cannot make the whole box neutral by
adding a counterion. Looking into literature, I've seen that it is possible
to solve the charged box issue in cp2k through Ewald, by smearing a
compensating background charge to have an overall neutral simulation box
(one for all, see Sprik et al JCTC 2011, 7, 1951.
http://pubs.acs.org/doi/pdf/10.1021/ct100715).

My question is: which exact input section should I look for ? I looked
around the Poisson solvers, but I don't feel confident I found the right
place. Other Ewald is in the MM section, but I don't think I've to run a
QM/MM if a I have a pure QM box.  In case it is in the Poisson section,
which keywords ? Further, I've not seen how to input the amount of the
background charge. Is this "understood" automatically by cp2k ?

Of course, any help on how to handle this issue, and how to check things
are done properly, is wellcome.

Thank you in advance,
Giancar
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