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Re: [ESPResSo-users] Mass scale in simulations

From: Georg Rempfer
Subject: Re: [ESPResSo-users] Mass scale in simulations
Date: Thu, 23 May 2019 21:14:56 +0200

I created a pull-request to clarify the offending section in the docs:

On Thu, May 23, 2019 at 9:00 PM Georg Rempfer <address@hidden> wrote:
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 <address@hidden> wrote:
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.


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."
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,

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