[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [ESPResSo-users] No conservation of momentum

From: Mingyang Hu
Subject: Re: [ESPResSo-users] No conservation of momentum
Date: Thu, 7 Apr 2011 13:20:09 -0400

Hi Marco,

If you want a momentum conservative thermostat, try DPD. It is basically implemented by adding paired noise on particle pairs, so zero net force.



Mingyang Hu
PhD Candidate
Department of Physics
Carnegie Mellon University

On Thu, Apr 7, 2011 at 1:14 PM, Ulf Schiller <address@hidden> wrote:
Marco Blanco wrote:
> Dear all,
> I'm doing a simulation on an NVT ensemble with a single polymer chain
> centered in the simulation box whose half-length is considerable larger
> than the maximum length of the polymer, so the chain doesn't interact
> with periodic images. I'm also setting the initial velocity of each
> monomer at 0, thus the initial momentum is zero too, and I'm not
> including any external force. From such initial setting, one expects
> that the net velocity of the system remains zero through the entire
> simulation, and the center of mass of the molecule doesn't move at all,
> only that the molecule folds/unfolds and rotates. However, when I run my
> simulation with Espresso, that doesn't happen. At the beginning I
> thought that it was because of the cut-off radius, so I set r_cut to a
> distance larger than the maximum length of the polymer, but the result
> was the same. I'm not very familiar with Langevin thermostats, so I
> don't know if the problem is my initial setting or if it is a
> pathological issue of the algorithm. I'd appreciate if someone can help
> me with this problem.
> Thanks,
> Marco


the Langevin thermostat is not momentum conserving - fluctuations of the
net momentum and diffusion of the center of mass are just what you would
expect for Brownian motion.


Dr. Ulf D. Schiller                         Building 04.8, Room 231a
Institute of Complex Systems (ICS-2)        Phone:  +49 2461 61-1765
Research Center Juelich, Germany            Fax:    +49 2461 61-2850

reply via email to

[Prev in Thread] Current Thread [Next in Thread]