Re: [ESPResSo-users] referring to stored configs separately

[Ulf Schiller]

Hi all,

On 03/26/2013 09:49 AM, Olaf Lenz wrote:
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> Hi Koen!
>
> On 03/26/2013 08:18 AM, Koen Nickmans wrote:
> > 1. When a lennard-jones potential is shifted so that the potential
> > is equal at a cutoff radius, how does espresso handle the
> > calculation of forces around the cutoff point? I cannot find where
> > this is discussed.
>
> The standard LJ potential in ESPResSo does have a discontinuity in
> the force at the cutoff radius. We do not handle the case otherwise. To
> my knowledge, this is only important when you choose the cutoff radius
> very small or want to simulate at very high accuracy. If you really need
> this, it should not be very hard to extend the LJ potential accordingly.
> We would be interested in that code if you write it.

Small addendum: If I'm not mistaken, it is a good idea to truncate the 
potential at the minimum. Otherwise energy conservation might be 
affected (NVE ensemble), and the minimum of the truncated potential may 
not be a point of zero force (which in turn might effect some energy 
minimization protocols). If the potential is cut off at a different 
point, one can 'taper' the potential to make its derivatives go to zero 
as well.

Best wishes,
Ulf

--
Dr. Ulf D. Schiller                        Building 04.16, Room 3006
Institute of Complex Systems (ICS-2)       Phone:   +49 2461 61-6144
Forschungszentrum Jülich, Germany          Fax:     +49 2461 61-3180

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