I am trying to compute the density of water. For a start I have just used a very small box consisting of 703 molecules. Using the NPT, I find that the box size increases dramatically ( nearly 200 times larger in each dimension), then reduces and increases again. The simulation becomes extremely slow. I started off with the correct box size for the density of water at 1 atm pressure, so I would expect to recover approximately this box size.
Is there something wrong with my input ? I am using TIP4P to model the water molecules.
in.swnt_c (1.04 KB)
data.swnt (215 KB)