[gmx-users] NVE of water
r.friedman at bioc.uzh.ch
Mon Mar 1 17:22:31 CET 2010
Berk Hess wrote:
> > Date: Mon, 1 Mar 2010 15:44:28 +0100
> > From: r.friedman at bioc.uzh.ch
> > To: gmx-users at gromacs.org
> > Subject: Re: [gmx-users] NVE of water
> > Mark Abraham wrote:
> > > On 2/03/2010 12:39 AM, Ran Friedman wrote:
> > >> Hi,
> > >>
> > >> I would still argue that double precision is important.
> > >
> > > Oh? The discussion of Table 4 of
> > > http://pubs.acs.org/doi/abs/10.1021/ct700301q (2008 GROMACS 4 JCTC
> > > paper) suggested to me that single-precision NVE could be done well in
> > > GROMACS. Am I missing something?
> > >
> > > Mark
> > "The presented benchmarks were performed in the NVT ensemble"
> (section IX).
> > Or am I missing something?
> No, but everything that affects energy conservation in NVE also
> affects it in NVT,
> in addition the thermostat affect the integration accuracy in NVT (and
> in NVT
> you do not measure energy conservation from the total energy, but from the
> conserved energy quantity).
> Double precision can be important for energy conservation, but often other
> factors deteriorate the energy conservation orders of magnitude from what
> can be reached in single precision already. Double precision is only
> for testing or when you really need to generate an NVE ensemble.
Thanks for clarifying Berk - I was referring to the latter (i.e., when
you really need to generate an NVE ensemble). I guess this is the main
reason to run with NVE. Since most people are not running NVE with large
systems or for production simulations, the added accuracy often
justifies the use of double precision.
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