[gmx-developers] [gmx-users] Wrong Nose-Hoover integrator

[Erik Lindahl]

Hi Berk,

Sounds great, but could you possibly send us the article as an 
attachement (or a reference to find it)? When I follow the link I only 
get a not-logged-in message.

Cheers,

Erik

On Mar 29, 2005, at 12:12 PM, Berk Hess wrote:

> Hi,
>
> I have implemented the correct Nose-Hoover leap-frog scheme as written 
> in:
> http://www.nrc.nl/binnenland/artikel/1111643830212.html
>
> But I have not been able to reproduce the incorrect 3.2.1 thermostat 
> work
> as reported by Michel.
> For a box of 216 waters with delta_t=0.002 and 0.9 nm RF I get correct 
> work
> at least up to tau_t=0.1 ps.
> Michel, how many waters, what cut-off scheme and what time step did 
> you use?
>
> The correct leap-frog algorithm (or probably any reversible 
> integration scheme)
> poses another problem.
> With dt=2 fs SPC water with a full step tempature of 300 K (determined 
> from v(t)),
> has a half step temperature of 297.8 K. With dt=4 fs the difference 
> will be much larger.
> The full-step temperature is the more accurate expression, but can not 
> be used
> in any simple integration scheme. This means that the temperature for 
> water
> simulations with reversible Nose-Hoover coupling will be off by at 
> least 0.7%.
> I am afraid this problem can not be solved.
>
> Berk.
>
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