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## Re: [ESPResSo-users] Mass scale in simulations

 From: address@hidden Subject: Re: [ESPResSo-users] Mass scale in simulations Date: Thu, 23 May 2019 10:59:33 +0800

Dear David,

In my opinion, if you don't activate the "MASS" feature, then all the particles have the same reduced mass of 1. And the resulting time scale is
[time] = [length] \sqrt{  [mass] / [energy] } as the document said.
So the time scale is  independent of the number of particles.

Regards!
Ricky

From: Geiseld
Date: 2019-05-22 18:10
Subject: [ESPResSo-users] Mass scale in simulations
Dear all,

I have a question concerning the mass scale of the simulations in espresso.
The documentation states that

"By default, ESPResSo uses a reduced mass of 1,
so that the mass unit is simply the mass of all particles."
(http://espressomd.org/html/doc/introduction.html#on-units)

How is this statement to be interpreted? Does the time scale of my
simulations change
when I add particles to the simulation, like

[time] = [length] \sqrt{ #particles* [mass] / [energy] }

or do I still only use the mass of one particle and assume that all
particles have the same mass?

To test this I constructed a simple simulation of diffusing particles
and calculated the
diffusion coefficient of a single particle (which should be
independent of the number of
particles in the box (no interactions)).
Here, it seemed as if the time scale was independent of the number of
particles. Is this correct?

I would be very thankful for advise,

best regards,
David.