Re: Constraint failure & velocity problem

From: Peter Freddolino (
Date: Tue Sep 02 2008 - 14:00:41 CDT

Hi Jack,
this usually means that either you haven't minimized long enough, or
you're using too long a timestep (or something along those lines that
makes your system unstable). Constraining the atoms whose motion is
becoming unstable is *not* a good solution to this. How have you set up
your system?

Shultz, Jack wrote:
> I was getting a bunch of Constraint failures, then I got most of them to
> disappear by setting the beta to 1 in the constraint and fixed atom file
> for all the problem atoms. I still get a constraint failure for one of
> them. I also don't know why I get this velocity error. Changing the
> temperature has no effect. Any ideas?
> TCL: Running for 250000 steps
> ERROR: Constraint failure in RATTLE algorithm for atom 2482!
> ERROR: Constraint failure; simulation has become unstable.
> ERROR: Atom 1207 velocity is 1.00258e+007 -1.17511e+007 -9.39458e+006
> (limit is
> 10000)
> ERROR: Atoms moving too fast; simulation has become unstable.
> ERROR: Exiting prematurely.
> ==========================================
> WallClock: 7.188000 CPUTime: 7.188000 Memory: 0 kB
> Program finished.

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