[gmx-users] Electrostatics and VDW

[David Mobley]

Una,

With PME, you don't have to have rlist<rvdw. You might, however, want to
have rlist slightly larger than rvdw. You don't have to, but since the
neighbor list is only updated every nstlist steps, if rlist is the same as
rvdw, you can run into the situation where an atom has moved inside the vdw
cutoff in a couple of steps, but your calculation doesn't realize it has
moved inside the cutoff until after nstlist steps. You can solve the
problem, of course, by using nstlist=1, but that could slow things down a
lot, so it may be better to simply use, say, rlist=1.1 and rvdw=1.0 so atoms
appear in the neighbor list before getting counted for vdw interactions.

David


On 1/24/06, Una Bjarnadottir <una.bjarnadottir at ucd.ie> wrote:
>
> Dear all,
>
> Just to have the content of this discussion clear
> http://www.gromacs.org/pipermail/gmx-users/2004-August/011683.html
> and all other discussion on this matter.
>
> When using coulombtype = PME  and vdw-type = Cut-off is it alright to
> have the;
>
> rlist=rvdw=rcoulomb = 1
> rvdw-switch=rcoulomb-swithc = 0
>
> Or does it have to be;
>
> rlist=rcoulmb = 0.9 and rvdw = 1.4
>
> Is the 2nd thing only for cut-off but not for PME?
>
> Thanks in advance for any replies, this is confusing me a lot.
>
> Una
>
>
>
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