[lammps-users] large change in volume during simulation of water using npt

I see a couple of issues.

  1. It doesn’t look like you converted your bond and angle coefs from real to metal units.
  2. I assume your pressure is meant to be 1 atm, but metal units are in bars so you need to convert.
  3. Why do you initialize your velocity at 800 K then run your sim at 373? That would cause your system to blow up then slowly contract back as it cools down.
  4. What was your starting density of water? Last I checked 373 was the boiling point of water. If you started with a liquid density of around 1 g/cm^3 and you’ve got gas, then there’s your reason for the 5 to 6 times expansion right there.