[gmx-users] Compressibility issue - real concern

[Erik Lindahl]

Hi,

On May 3, 2007, at 12:37 PM, Jones de Andrade wrote:

> Hi Berk! Thanks for your so fast answer!
>
> I'll try to look for a different tau_p. I would really feel 4 ps a  
> too high value, even for water systems, but will look around before  
> decision. Anyway, I'm still concerned about the compressibility value.
>
> Long time ago in this list I came to this question, and this is how  
> this ended:
>
> > Hi,
> >
> > Just use the water value for any liquid system (5e-5 or so).
> >
>
> > As the manual explains, it only affects the coupling time, not the
> > equilibrium pressure.
> >

This is valid for long times, and (as always for pressure) assumes  
the external coupling to be clearly slower than the internal  
dynamics. I have no idea how Amber or DLPOLY sets their tau_t with  
Nose or Parinello-Rahman, but as specified in the Gromacs manual we  
use the period of average fluctuations at equilibrium. With tau=0.1  
the system will very likely never reach that equilibrium.

Cheers,

Erik

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20070503/a108f08c/attachment.html>