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

 From: geiselda Subject: Re: [ESPResSo-users] Mass scale in simulations Date: Fri, 24 May 2019 08:31:58 +0200 User-agent: Horde Application Framework 5

Dear Georg,

thank's for clarification.
Have a nice day and weekend!

David!


I think I might be the last one to touch that part of the documentation. I
meant to say exactly what Ricky took from it: The time scale does depend on
the mass of an individual particle, and not the combined mass of all
particles. The time scale therefore is independent of the number of
particles. Sorry for the confusion.

On Thu, May 23, 2019 at 5:00 AM address@hidden <


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

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*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.