I cannot make MD simulation constant in pressure

From: Faramarz Joodaki (fjoodaki_at_my.uri.edu)
Date: Mon May 23 2016 - 14:41:54 CDT

Hi Everyone,

I am using langevin to make temperature constant and langevinPiston to make
pressure constant in my MD simulation. Some parts of my configuration file:

# Constant Temperature Control
langevin on ;# do langevin dynamics
langevinDamping 1 ;# damping coefficient (gamma) of 1/ps
langevinTemp $temperature
langevinHydrogen off ;# don't couple langevin bath to hydrogens

# Constant Pressure Control (variable volume)
useGroupPressure no ;# needed for rigidBonds
useFlexibleCell no
useConstantArea no

langevinPiston on
langevinPistonTarget 1.01325 ;# in bar -> 1 atm
langevinPistonPeriod 200.0
langevinPistonDecay 200.0
langevinPistonTemp $temperature

During simulation, the pressure is fluctuating which is fine! I calculated
the average pressure over MD simulation, and it is about 13atm which is not
equal to my desire 1atm pressure.

I would be so grateful if anyone could guide me with this matter.

Best Regards,

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