recentering option for isolated system calculations

Axel akoh... at
Tue Mar 4 23:21:50 UTC 2008

On Mar 4, 5:29 pm, Rad <rad.... at> wrote:
> Axel,
> I am struggling with a large isolated system and I am using the MT
> poisson solver. Maybe I should try the wavelet based PS. Could you
> please let me know how to set up the section and if there are any

syntax and parameters is in the cp2k input reference manual.

BTW: it would be nice to have an explanation for the requirement
of FFTSG as preferred FFT, it seemed to work with FFTW3 as well and
i would have expected the code to crash or refuse the run, if
this was a "hard" requirement.

> caveats? (Teo mentioned that and I forgot the syntax) Do we have to
> have
> a vaccum of 20% for the wavelet method or is it only for the MT
> scheme?

i would consider 20% vacuum (how do you compute it?) to be far too
little for MT p-solver. you may get away with it if your system has
favorable error cancellation, but i would not depend on it.

formally, the MT p-solver requires a box of twice the size of a
sphere that encloses the total charge density of your molecule
(i.e. atoms _and_ electron density). i can see small errors crop
up on my (weakly interacting) test system starting from exactly
the %50 mark and then the errors became intolerably large at
having 40% vacuum.


> Thanks
> Rad

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