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


From: Ulf Schiller
Subject: Re: [ESPResSo-users] referring to stored configs separately
Date: Tue, 26 Mar 2013 10:15:31 +0100
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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 J├╝lich, Germany          Fax:     +49 2461 61-3180


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