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Re: [ESPResSo-devel] harmonic potential

From: Torsten Stuehn
Subject: Re: [ESPResSo-devel] harmonic potential
Date: Wed, 22 Oct 2008 12:53:57 +0200
User-agent: Thunderbird (X11/20080213)

Hi Axel,

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


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?


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

Tel.  +49-(0)6131-379268
Fax +49-(0)6131-379100 EMail address@hidden

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