[gmx-users] Pressure calculated from g_energy showing negative value

Sunita Patel sunita at chem.iitb.ac.in
Mon Oct 27 08:14:01 CET 2003

Dear gmx-users,

In the .mdp file I have included following parameters for pressure

pcoupl                            = berendsen
tau_p                             = 0.5
compressibility                   = 4.5e-5
ref_p                             = 1.0

 From g_energy calculation I got negative value of pressure with large
fluctuation. What could be the  reason for this ?

The presure vs time  plot I have send as an attachment.

The following is the output which I got after the g_energy calculation of

Statistics over 500001 steps [ 0.0000 thru 1000.0001 ps ], 1 data sets

Energy                      Average       RMSD     Fluct.      Drift
Pressure (bar)              1.01185    161.177    161.176 0.00204041

I will grateful if  anyone explains its reason.

Sunita Patel

Sunita Patel
Biophysical Lab.,
Dept. of Chemistry,
Indian Institute of Technology(IIT) Bombay,
Powai, Mumbai, Maharashtra,

Tel: (91)-22-25764176.
Email:sunita at chem.iitb.ac.in

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