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Re: [ESPResSo-users] force acting on particles using Langevin thermostat

From: Axel Arnold
Subject: Re: [ESPResSo-users] force acting on particles using Langevin thermostat
Date: Fri, 24 Oct 2014 23:44:49 +0200

Dear Xikai!

On 24.10.2014, at 17:43, Xikai Jiang <address@hidden> wrote:

Dear all:

I have a rather naive question about the force I printed out during a simulation using Langevin thermostat using the following command:

part ID print force

I'm wondering will the outputed force is the summation of the force due to potential, a friction force and a random force? If yes, is there anyway to print out only the force due to potential?

The force loop computes all contributions. And because in ESPResSo the thermostat is just one of the acting forces, this is included in the overall forces that part print force returns. To print out the forces not including the thermostat, you need to temporarily switch it off as follows:

set term [thermostat]
thermostat off
integrate o
part ID print force
eval thermostat [lindex $term 0]

This will switch off the thermostat and reset it after read out. This is admittedly somewhat complicated, but worthwhile, because the random forces can be much larger than what you actually want to measure.


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