fix npt

Dear all,
I have question regarding the fix npt.
I have a 3D system of liquid crystal (70 LC in a periodic 3D box ). I want to simulate it under total 1 atm pressure.

fix 1 mol npt temp 298.0 298.0 100.0 iso 1.0 1.0 1000.0
Is this command perfect? Because when I use the command compute pressure it does not show pressure 1 atm. I am working in real unit.
With best regards,
Pritam

Pressure is noisy. Your damping constant of 1000.0 means you will

need to run many ps to get an equilibrated system (assuming you

are doing everything else right). What is the time averaged value

of pressure after equil and after running many more ps?

Steve

It is important to recognize that when you run NPT or constant-pressure dynamics, the instantaneous system pressure reported by LAMMPS is never constant. What is constant is the pressure in the fictitious reservoir whose volume is coupled to that of the simulation cell. In response to the constantly changing pressure difference between the simulation cell and the constant-pressure reservoir, volume is allowed to “flow” back and forth between them. If you run long enough, averaging over many cycles of the back-and-forth volume flow, the average pressure in the simulation will closely match that of the reservoir.