Re: Atoms moving too fast

From: Marcos Sotomayor (
Date: Tue Dec 06 2005 - 13:43:54 CST

Hi Eric,

First of all, it would be good to know if you are able to restart your
simulation without cooling the system (if that works, then we can isolate the
problem and explore the method you are using to cool the system). It would
be good to know what methods are you using to control the temperature
(Langevin before cooling? what is your target temperature?) and pressure,
what time step are you using, if you have any constraint applied to any
part of the system, and also check if your periodic boundary conditions
are properly set. Usually, the "Atoms moving too fast" error is caused by
atoms that are overlapped (poor minimization, wrong boundary conditions)
or other issues with your configuration file , more information about
your particular setup is needed to tackle your problem.


On Tue, 6 Dec 2005, Eric Perim wrote:

> Hello,
> I posted a message about having problems with my simulation, and
> followed the advice given by Lewyn of doing a longer simulation. I
> just finished doing an 1000000 timestep (1ns) equilibration (constant
> temperature and pressure) of my system, but still I get an error
> message saying the atoms are moving too fast when I try to start
> another simulation, this one to cool the system (using tcouple). The
> end of the log file is as follows:
> ENERGY: 980000 5007.0883 3041.1113 146.1419
> 14.6181 -59797.6788 6167.0269 9451988.1543
> 0.0000 13539.6654 9420106.1274 310.1190
> 9420679.0896 9420679.0896 310.1190 -3082206.2226
> -3081720.6492 142397.7388 -3082206.2226 -3081720.6492
> ERROR: Atom 6478 velocity is -401.956 -4511.72 16669.9 (limit is 10000)
> ERROR: Atoms moving too fast; simulation has become unstable.
> ERROR: Exiting prematurely.
> ==========================================
> WallClock: 16.802896 CPUTime: 10.117187 Memory: 7665 kB
> I'd like to know if anyone know how to solve this, since I can't
> carry on my research without doing these simulations.
> By the way does anyone know where can I get a routine for
> calculating the pair distribution of the system after simulation?
> Thanks in advance,
> Eric

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