Re: [ESPResSo-devel] harmonic potential

[Torsten Stuehn]

Hi Axel,

I vote for a 2.0*r default cutoff for the harmonic bonds. This should be large 
enough
for most cases. As Christoph proposed, we could use a negative cut off for "no cut 
off".
Then we don't need an additional switch for this.

Torsten.

Axel Arnold wrote:
> Hi all,
>
> currently, there is a problem with the harmonic potential on multi-processor 
> systems: to calculate any bonded potential, both bonding partners need to be 
> on the same processor, at least as a ghost. To ensure this, the maximal 
> cutoff needs to be larger than the distance of the two bonding partners. For 
> the harmonic potential, this distance can in general be infinite; but 
> currently, the maximal cutoff is only set to the _minimum_ of the harmonic 
> potential.
>
> There are some solutions:
> - use the skin to increase the max_cutoff: Bad idea, since Espresso will then 
> create huge Verlet lists, and on the other hand, particles can move at most 
> skin/2 before the ghost shells are recalculated, leaving essentially the same 
> problem.
> - give the harmonic potential also a breaking distance, not only a minimum: 
> that is, we specify a second length, after which the potential breaks. That 
> will however change the syntax of the harmonic potential, although we could 
> provide a default (e.g. 2*r). In addition, we could also provide a switch to 
> turn off breaking. At least on single processors, a harmonic bond would never 
> break.
>
> Any votes? Suggestions?
>
> Axel


--
Dr. Torsten Stühn
MPI für Polymerforschung
Ackermannweg 10
55128 Mainz / Germany

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