[CP2K:2005] Re: counter charge

Jun Cheng chen... at googlemail.com
Tue Apr 21 10:42:30 UTC 2009

Thanks, Axel.

Sorry for the late reply.

On Sat, Apr 18, 2009 at 3:48 PM, Axel <akoh... at gmail.com> wrote:

> those fractional charges could be provided as pseudopotentials.
> there are DFT codes that allow you to have "fractional hydrogens"
> to terminate polar surfaces.
> since cp2k also supports all electron calculations, you could add an
> all-electron entry with a fractional charge and then define an empty
> basis set for that atom type.

however, i would be very careful with a setup of that kind. if the
> "fractional atom" is too close to other atoms you may get spill-out,
> and many people that program quantum codes tend to implicitly or
> explicitly
> assume that electrons and charges are integer throughout and thus
> you may get unexpected results and should run careful tests on easy
> to debug test systems. i am certain that cp2k developers would be
> happy to get feedback and test inputs on that subject.

I tried to change the charge of all electron H pseudopotential to a
fractional, cp2k complained:
an integer type object was expected.
So, the present plan is to use H (integer charged) with modified
pseudopotential which keeps electrons
away. Since the H is just used as counter charge and will not be close to
the rest of system, I am not
worried about the spill-out of electrons. I am still working on how to
modify the pseudopotential of H. If
someone knows how to do this, I am greatly appreciated if letting me know.
Many thanks in advance.

other than that, it might be easier to discuss options, if you could
> produce an example input illustrating your setup and ideally also an
> example input for a code that does support what you want to do, or
> a paper describing such a calculation.

I am sorry I don't know other codes being able to calculate fractional
hydrogens and haven't found a paper doing similar things yet.
I will get back to you once I work it out.

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