Re: Constant pressure contril

From: Sichun Yang (syang_at_physics.ucsd.edu)
Date: Sat Feb 28 2004 - 18:32:31 CST

Thank you for your explanation, Jerome.
However, How can I understand a negative GPRESSURE?

On Sun, 29 Feb 2004, [iso-8859-1] Jérôme Hénin wrote:

> Hello Sichun,
>
> The GPRESSURE field should fluctuate around the requested value (if you
> specified the useGroupPressure option). However, the fluctuations are HUGE,
> because (1) the system is microscopic and (2) it's in a condensed phase. So
> don't worry if the pressure is 100 times too high at times (depending on
> system size).
> What's relevant is computing averages of this value over large times. Then you
> should get *roughly* the pressure you asked for.
>
> So as you can see, "constant-pressure" is a strange expression for what we're
> simulating. But what does "pressure" mean in the first place, when you're
> speaking of, say, 50000 atoms in a 10 ns trajectory? We can't ask too much
> regarding macroscopic (or even mesoscopic) quantities...
>
> Cheers,
> Jerome
>
> Le dimanche 29 Février 2004 00:05, Sichun Yang a écrit :
> > Dear All,
> >
> > I have used Nose-Hoover Langevin piston pressure ON.
> > Now I want to double-check and make sure my configuration is ok.
> > Which pressure should be constant in the output file, PRESSURE
> > or GPRESSURER? It seems none of them is close to constant in my output.
> > Any hint? Thanks,
> > Sichun
>
> --
> Jérôme Hénin
> Equipe Dynamique des Assemblages Membranaires
> Université Henri Poincaré / CNRS UMR 7565
> B.P. 239 54506 Vandoeuvre-lès-Nancy Cedex
> Tel : (33) 3 83 68 43 95 Fax : (33) 3 83 68 43 71
> http://www.edam.uhp-nancy.fr/
>
> In principio creauit Linus Linucem
>
>

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