[gmx-users] Conserved energy

Peter C. Lai sirmoo at cowbert.2y.net
Fri Aug 19 13:03:38 CEST 2005

On Thu, Aug 18, 2005 at 06:12:38PM -0300, Alberto Malvezzi wrote:
> Dear friends,
> one way to verify the stability of trajectories is to follow if the 
> total energy of the sistem is being conserved.
> Since numerical fluctuations cannot be avoided, how much can the values 
> fluctuate (drift), and still the energy be considered conserved?
> If any one knew a reference on this topic I would be happy.
> Thanks.
> Alberto

In an NVE ensemble, the total average energy shouldn't increase as
the simulation progresses. You can test the validity and tolerance by
varying your timesteps and repeating the simulations to find the
longest timestep you can use with minimum drift. Anton and Berk have 
covered this and other methods to minimize drift (tweaking cutoffs)
in J. Comput. Chem. (1999) 20 (8), 786-798.

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Peter C. Lai

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