Re: [ESPResSo-devel] Mass Dependent Diffusion in Langevin Thermostat

[Ulf Schiller]

I agree and the obvious source is the Langevin noise - one only has to
look at the units to see that it's wrong...

On 18/06/15 10:42, Joost de Graaf wrote:
> Dear All,
> 
> Just a quick check before I open a bug report. In my understanding the
> friction coefficient in the Langevin thermostat is supposed to represent
> 
> $\zeta = 6 \pi \eta R$
> 
> and therefore, the diffusion coefficient in LD should not depend on the
> mass of the particle. However, in ESPResSo, the behavior is different,
> see attached MSD.png. Is this because we choose a different way to
> define the input parameter for the Langevin thermostat? I did not find
> anything on it in the UG, so I think the ESPResSo behavior is wrong --
> but if anyone can come up with a good argument as to why it should be
> this way, I'm listening.
> 
> If such fundamental things are broken, we should check the rotational
> diffusion, and other simple aspects of ESPResSo as well.
> 
> Kind Regards, Joost


-- 
Dr Ulf D Schiller
Centre for Computational Science
University College London
20 Gordon Street
London WC1H 0AJ
United Kingdom

Phone: +44 (0)20 7679 5300