Error with tclBC to induce shear flow

From: KONG Xian (
Date: Thu Oct 20 2011 - 20:59:42 CDT

Dear NAMD experts:

         I am using TclBC to induce the a shear flow as the tutorial says.
And all the parameters are as in the tutorials.

         However, when the simulation last 3ns, it stoped for a ERROR says
that some atom velocity is too large.


ERROR: Atom 24730 velocity is 714286 -12.147 19.1932 (limit is 6000)

ERROR: Atom 24731 velocity is -5.66934e+06 63.4502 -182.21 (limit is 6000)

ERROR: Atom 24732 velocity is -5.66922e+06 56.0542 -181.219 (limit is 6000)

ERROR: Atoms moving too fast; simulation has become unstable.

ERROR: Exiting prematurely; see error messages above.


I decrease the force in the configuration file from 2 to 0.5, the simulation
stopped after a longer period(6ns).

So, I wonder whether it is common for the nonequilibrium MD or I made some
mistake in my modeling?

Thanks a lot for any help or suggestion.


Best wishes,



Tsinghua University, Beijing, China


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