[gmx-users] energy drift - comparison of double and single precision

Michael Shirts mrshirts at gmail.com
Fri Oct 11 20:45:30 CEST 2013

Hi, Guillaume-

No one can tell you if you did anything wrong if you didn't tell us
what you did!  There are literally thousands of combinations of
options in running an NVE simulation, a substantial fraction of which
are guaranteed not to conserve energy.

If you post the files (inputs and relevant output files) to
redmine.gromacs.org, then people would be able to see if it was an
error in how you ran the simulation, or an actual bug.

On Fri, Oct 11, 2013 at 1:58 PM, Guillaume Chevrot
<guillaume.chevrot at gmail.com> wrote:
> Hi all,
> I recently compared the total energy of 2 simulations:
> lysozyme in water / NVE ensemble / single precision
> lysozyme in water / NVE ensemble / double precision
> ... and what I found was quite ... disturbing (see the attached figure -
> plots of the total energy). I observe a constant drift in energy in the
> case of the single precision simulation.
> Did I do something wrong*? Any remarks are welcomed! I join the ‘mdout.mdp’
> file so you can check what mdp options I used.
> My second question is: if I did not do something wrong, what are the
> consequences on the simulation? Can I trust the results of single precision
> simulations?
> Regards,
> Guillaume
> *PS: I am not the only one encountering this behavior. In the literature,
> this problem has already been mentioned:
> http://jcp.aip.org/resource/1/jcpsa6/v126/i4/p046101_s1
> --
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