[gmx-users] Semi-isotropic pressure coupling

[Berk Hess]

Hi,

You X-Y area does not change because your X-Y compressibility
is ridiculously small.

BTW does somebody know why certain emails on the mailing list have
the personal email address set as reply-to, instead or the mailing list?

Berk.


> Date: Wed, 14 May 2008 11:18:37 -0400
> From: jamads at rpi.edu
> To: gmx-users at gromacs.org
> Subject: [gmx-users] Semi-isotropic pressure coupling
> 
> 
> Hi,
> 
>  I was performing NPT simulation of a water - solid interface and used
> Berendsen Semi-Isotropic coupling. The solid is a SAM - 11 atoms long and 
> packed together closely to form a surface in the x-y plane.
> 
>    
> Pcoupl              =  Berendsen
> Pcoupltype          =  semiisotropic            ; pressure geometry
> tau_p               =  0.5  ; p-coupling time
> compressibility     =  1e-15  4.5e-5
> ref_p               =  1.0  1.0 ; reference pressure
> 
> The simulation runs and the box doesn't distort nor does the X-Y area
> change. However, when I calculate the pressure using g_presure, this is
> what I get 
> 
> Energy         Average       RMSD     Fluct.      Drift  Tot-Drift
> -------------------------------------------------------------------------------
> Pressure-(bar) 10002.5    270.246    266.208 -0.0806168   -161.234
> Pres-XX-(bar)  15670.1    538.695    534.178  -0.120572   -241.143
> Pres-YY-(bar) 14335.4    451.628    447.136  -0.110053   -220.106
> Pres-ZZ-(bar) 1.03256    238.912    238.824 -0.0112258   -22.4517
> 
> Why is the pressure so different from the reference pressure in the
> lateral directions.  Is this the pressure in the solid or in water? 
> 
> 
> 
> 
> 
> 
> 
> 
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