[gmx-users] Pressure in NPT simulation

[Mishelle Oña]

Hello,

I have a question concerning pressure. I runned a NPT simulation with the following parameters:

; Pressure coupling
Pcoupl                   = Berendsen
Pcoupltype               = Isotropic
tau_p                    = 1.01325
compressibility          = 4.5e-5
ref_p                    = 1.01325
When analyzing the average pressure using g_energy I got this results:
Energy                      Average   Err.Est.       RMSD  Tot-Drift
-------------------------------------------------------------------------------
Potential                   -128613        9.9    363.247   -65.2445  (kJ/mol)
Kinetic En.                 24189.2        1.4    242.381   -6.10124  (kJ/mol)
Total Energy                -104424         11    440.485   -71.3457  (kJ/mol)
Temperature                 300.544      0.018    3.01152 -0.0758065  (K)
Pressure                    323.536       0.65    244.361   -3.94119  (bar)

I wonder why the simulation cannot descent to the ref_p value. It is a system of a polymer in a box full of water.
 Thanks for the answer and help.
Mishelle