target pressure value

From: Namd Namd (
Date: Tue Jan 17 2012 - 06:30:20 CST

Dear namd people, I performed 5 ns md simulation for water molecules in NPT ensamble to equilibrate the system. Target pressure is 1 atm and the values in conf file are   # Constant Temperature Control langevin            on    langevinDamping     5     langevinTemp        $temperature langevinHydrogen    on        # Constant Pressure Control (variable volume) useGroupPressure      no useFlexibleCell       yes  useConstantArea       yes    langevinPiston        on langevinPistonTarget  1.01325 ;#  in bar -> 1 atm langevinPistonPeriod  200. langevinPistonDecay   100. langevinPistonTemp    $temperature     I found the density of water to be 1 g/cm3 but I couldn’t reach the target pressure value. The pressure vs timestep graph file is in attached and fluctuation is too high. Could you please explain the reason of it ? What should I do also to reach the target pressure value ( 1 atm ) ?   Best regards.


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