[gmx-users] confused about rcoulomb<=rlist
dmobley at gmail.com
Wed Jul 12 16:58:23 CEST 2006
I desperately need some clarification about how GROMACS handles
coulomb interactions with rcoulomb and rlist, and why it makes sense
to do things this way.
In particular, there was a thread on the revisions list
a while back explaining that in 3.3.1, grompp checks to ensure that
rcoulomb=rlist for PME/Ewald/PPM. I was very surprised by this, as I'd
always been using rlist>rcoulomb, which I thought was best. Can
someone explain why one would want rcoulomb=rlist? I don't quite
understand the explanation on the revisions/developers list.
My confusion is exacerbated by the fact that the GROMACS 3.3 manual
includes the following statement:
"The neighbor search cut-off rlist should be 0.1 to 0.3 nm larger than rvdw
to accommodate for the size of charge groups and diffusion between neighbor
This is exactly the same logic I was applying to rcoulomb when I
concluded that I wanted to make sure rlist was larger than rcoulomb --
basically, that I didn't want things outside rlist diffusing to within
rcoulomb between neighbor list updates, and hence not being counted in
the real-space interactions when they should be. Is there some other
concern that outweighs this or means that this point is irrelevant?
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