From chemistry-request@ccl.net Tue Mar 10 04:57:07 1992
Date: Tue, 10 Mar 92 00:55:11 -0800
From: ross@zeno.mmwb.ucsf.EDU (Bill Ross)
To: chemistry@ccl.net
Subject: mpp & nonbonded cutoffs
Status: R

Ray Cline mentions using a distance cutoff for vdw interactions
for efficiency and for speed of light interactions (event horizon)
for correctness.

My question:

What do people think of the utility of nonbonded cutoffs for avoiding
periodic imaging in periodic boundary conditions?

Another thought:

	Ray Cline: ... Even if you use "infinite" range potentials,
	you must remember that force interacts at the speed of light (3 x
	10^18 angstroms/sec) and given a timestep of 10^-16 seconds would mean
	that you should still limit "infinite" potentials to a cutoff of a few
	hundred angstroms. 

But you could further imagine marching in waves of forces from nested
few hundred angstrom shells from previous steps: a freight train
leapfrog algorithm (think of the memory & communication bandwidth required).

Bill Ross