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

[Mark Abraham]

On Oct 11, 2013 7:59 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.

Maybe. Unfortunately we cannot configure the mailing list to allow people
to send attachments to thousands of people, so you will need to do
something like provide links to files on a sharing service.

>
> 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?

Yes, as you have no doubt read in the papers published by the GROMACS team.

> 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

... which is six years old, examining the properties of code seven years
old. Life has moved on! :-) Even if you have found a problem, it is a big
assumption that this is (still) the cause.

Mark

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