[gmx-users] Pressures after NPT

[ibrahim khalil]

dear gromacs users, I did an NPT equilibration of 100ps with a reference
pressure of 1bar. After the equilibration, my average pressure was 1.2 bar.
But when I started my production run (with a reference pressure of 1 bar)
my pressure was rising (and falling) again. for the first 50 ps, the
average pressure was -7.2 bar. Then after a 100ps of production run the
pressure was -0.84 bar.

I have two questions regrading this-

1. Does negative pressure mean anything wrong with my system? or should I
just take the magnitude of my pressure?

2. After the NPT my average pressure was rising again(but eventually came
close to its reference value after some time), should it happen in a stable
simulation?