Re: [ESPResSo-devel] Particle Masses definition

[Ulf Schiller]

On 22/06/15 12:34, Evyatar Arad wrote:
> Good week all,
> 
> I’ve noticed that in friction_thermo_langevin there are two different masses 
> used in the langevin equation while calculating force:
>       p->f.f[j] = langevin_pref1*p->m.v[j]*PMASS(*p) + 
> langevin_pref2*gaussian_random()*massf;
> 
> What is the difference between PMASS(*p) and massf?
> both are available even though MASS (mass per particle) is off.

The variable `massf` is defined a few lines up in the code

  double massf = sqrt(PMASS(*p));

Note that the mass only enters this equation when the parameter gamma is
not a proper friction coefficient but a relaxation time. See also
https://savannah.nongnu.org/bugs/index.php?45349

Cheers,
Ulf

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