I see a couple of issues.
- It doesn’t look like you converted your bond and angle coefs from real to metal units.
- I assume your pressure is meant to be 1 atm, but metal units are in bars so you need to convert.
- 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.
- 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.