For studying effects of cut-off and integration setup on the results
I can see that one would to be able to set rcoulomb < rlist.
This is, however, not easy to implement exactly.
An exact cut-off would produce an infinit force at the cut-off.
Perhaps I'm a little confused here. Right now, isn't there an abrupt
cutoff at rlist anyway? So the abrupt cutoff is just being moved
inward? I suppose there's some technicality of the splines used to
generate the real space part, however. . .
But since we use spline interpolated tables, there will always
be some smoothing of this cut-off.
I think that with the current table setup there is no way to
have exact cut-offs.
Another option would be to apply a switch function to the PME
real space interactions.
Addionally one would want to set beta independent of rlist.
Right, one should be able to tune this independent of your
neighborlist cutoff for various reasons that David discussed.
So the only reasonable option I can think of is to implement
a new coulombtype = PME-switch, but with a note that this
is mainly useful for testing purposes and the normal PME
will give more accurate results.
Actually, I can imagine situations where extremely good energy
conservation (for multi ns runs) is important, and this option might
be useful -- you would trade a bit of accuracy for better energy
conservation.
Best,
Michael
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