[gmx-users] question: negative pressure

[David van der Spoel]

lugalzagissi wrote:
> Hello.
> 
> My problem is the next:
> I ran the 5 ns simulation of a molecule of polyethylene C1000 with pressure coupling under the temperature of 1000K. The parameters for p.coupling are the next:
> 
> Pcoupl                   =  berendsen
> Pcoupltype               = isotropic
> tau_p                    = 1.0
> compressibility          = 4.5e-5
> ref_p                    = 1.0
> 
> The average pressure for all the simulation is negative. These results I've got with g_energy:
> 
> Energy                      Average       RMSD     Fluct.      Drift  Tot-Drift
> -------------------------------------------------------------------------------
> Potential                   25695.5    347.159    341.527   0.117271    215.748
> Kinetic En.                 24928.9    294.821    294.818 0.00230749    4.24516
> Total Energy                50624.4    184.928    173.682   0.119579    219.993
> Temperature                  999.58    11.8215    11.8214 9.2524e-05   0.170219
> Pressure (bar)           -0.0807379    41.7124    41.7124 1.04028e-05  0.0191384
> Volume                      946.272    29.3151    1.62577 -0.0551136   -101.394
> 
> Could anybody explain, why?

this is fine. just look at the error bar.
> 
> Thanks
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-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,  	75124 Uppsala, Sweden
phone:	46 18 471 4205		fax: 46 18 511 755
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se
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