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1

Hi Users,

I’m running a simulation with atom_style angle and units real. Basically I’m trying to determine morphology of phase separated block copolymers. When I set up the simulation, it looks like I’ve filled all of the simulation space, however, once the simulation has run and the system reaches a semi-equilibrium, I get huge holes and the pressure is in the negative. I figure this is from the chains packing and arranging into a more dense state. So the question is, is it possible to determine the optimal starting density with just the LJ parameters or change the simulation box size so the pressure is 1 atm?

Thanks for any help and if you need more information, please feel free to ask!

Casey

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The density is a result of the morphology, so if you don't know it up
front, you don't know the density either. Why don't you just run in
NPT ensemble until the system is equilibrated?

Cheers,
      Axel

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Axel,

That’s a great idea! I’m new to MD so still learning the ins and outs.

Let’s see if I have this correct. If I want an NPT fix with a pressure of 1 atm by varying in the Z-axis and a temp of 300 K:

units real
timestep 1.0

fix 1 all npt temp 300.0 300.0 100.0 z 1.0 1.0 1000.0

Thanks for the help.