Re: Constant pressure contril

From: Jérôme Hénin (
Date: Sun Feb 29 2004 - 02:41:07 CST

Le dimanche 29 Février 2004 01:32, vous avez écrit :
> Thank you for your explanation, Jerome.
> However, How can I understand a negative GPRESSURE?

The pressure is computed as two components : the kinetic part is identical to
the ideal gas pressure (ie kT/nV - this one is of course positive, and nearly
constant), and the dynamic part, often computed using a virial expression (a
sum on all atoms of force_on_atom scalar position_of_atom). This second part
is the one with large fluctuations (which are smaller if you consider atom
groups rather than isolated atoms, that is, "group pressure"), and it takes
either positive or negative values.
Physically speaking, a system of interacting particles has a negative pressure
whenever it tends to shrink rather than to expand - this never happens to an
ideal gas, of course.


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
In principio creauit Linus Linucem

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