[gmx-users] neighbor list

[m b]

Berk Hess wrote:

> These charge groups are important for simulations with cut-off 
> electrostatics as they
> reduce the cut-off noise significantly.

its not so much about the noise, the point with charge
groups is that you end up with electrostatic interactions 
between only dipoles (which go with 1/r^3) and no
more monopole-monopole interactions ( 1/r ).
Thus the electrost. interaction is (seeemingly) shorter ranged 
(though still not converging for r-cut -> infinity) giving 
results that are less system-size dependent; whether they
are correct is a different question ...

but there still is the question: is in Gromacs only the generation 
the neighbour-list group-based or also the calculation of
the electrostatic interactions (which is nor necessarily the same
thing)

> With shiftted electrostatics or PME charge groups are only important for 
> performance reasons.

I am not sure whether group-based cut-off in combination
with PME is a good idea, and If you don't use PME there are 
still reasons to avoud group-based cut-offs, see, e.g., 
Biophys J, September 2000, p. 1537-1553, Vol. 79, No. 3;
there is also a more rigorous investigation of the subject 
by Hummer G., the exact reference eludes me for know ...

cheers
mic



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