[ESPResSo] Working with Offset Potentials

[Lorenzo Isella]

Dear All,
I am trying to run simulations with a very deep Lennard-Jones
potential (actually, I am using lj-cos2, which goes smoothly to zero),
but after setting the potential offset r_off to a non-zero value, I am
experiencing problems.
Mainly, I get this kind of warning:


0: LJ-Warning: Pair (3-6) force=87080447034401929425695277056.000000
dist=1.001203
background_errors 0 {086 particle coordinate out of range, image box =
-2147483648} {086 particle coordinate out of range, image box =
-2147483646} {086 particle coordinate out of range, image box =
-2147483648} {086 particle coordinate out of range, image box =
2147483646} {086 particle coordinate out of range, image box =
-2147483648} {086 particle coordinate out of range, image box =
-2147483642}

and then the simulation crashes. I think this is due to the fact that
sometimes the distance between two particles falls below r_off
(clearly everything depends on the r_off, since setting it to zero
removes my problem).
I have tried reducing the simulation time-step with little success.
I wonder if I should go on choosing a smaller and smaller time step or
there is a better way of handling this within Espresso.
Many thanks

Lorenzo