I’m trying to simulate a box of rigid SPC water molecules in NPT ensemble.
However during the process, the pressure always changes dramatically
from hundreds to thousands. Besides, the total energy is negative.
Below is relevant part of the input script. Any help or guidance would be appreciated.
boundary p p p
velocity all create 298 12432 dist uniform
fix 1 all shake 1e-6 500 0 m 15.994
fix 2 all npt temp 298 298 500 iso 3173 3173 500