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Re: [ESPResSo-users] Particle size distribution

From: Peter Košovan
Subject: Re: [ESPResSo-users] Particle size distribution
Date: Thu, 16 Apr 2015 14:00:03 +0200

Hi Miljena,

first of all, you need to specify what you mean by "particle size":
(i) effective hydrodynamic size, i.e. friction coefficient
(ii) effective size that matters for excluded-volume interactions
Depending on the physics of your system, you may need (i), (ii) or both.

(i) you need to set gamma per particle as you describe, and you need Espresso compiled with LANGEVIN_PER_PARTICLE activated, as pointed out by Hender Lopez. Also, note that when dealing with diffusion properties, Langevin thermostat is not the best choice as it screens hydrodynamics.

(ii) you need to modify the parameters of the short-range interaction potential that you use, e.g. in the LJ potential you would vary sigma or add some cutoff.



2015-04-16 13:54 GMT+02:00 Hender Lopez <address@hidden>:
Hi Milena,

You have to add LANGEVIN_PER_PARTICLE in your myconfig.hpp to activate
the individual friction coefficient. I have been use it and it works
fine for me.



On Thu, Apr 16, 2015 at 12:50 PM, Milena Smiljanic
<address@hidden> wrote:
> Hi,
> I am trying to run simulation with particles that have different diameters
> (what means with different friction coefficients), in combination with
> Langevin thermostat. I found in ESPResSo's user guide: part pid [gamma g ] -
> sets the nondimensional frictional coefficient gamma individually for the
> particle with id, but in my case it returns an error message:
> unknown particle parameter "gamma"
> while executing
> "part 0 pos 5 5 5 type 0  gamma 0.033"
> I've tried only with those features BOND_ANGLE, COLLISION_DETECTION,
> Is there another way to define different particle size?
> With kind  regards,
> Milena
> --
> Milena Smiljanic
> address@hidden

Dr. Peter Košovan

Departmtent of Physical and Macromolecular Chemistry
Faculty of Science, Charles University in Prague, Czech Republic

Katedra fyzikální a makromolekulární chemie
Přírodovědecká fakulta Univerzity Karlovy v Praze
Tel. +420221951290
Fax +420224919752

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