[gmx-users] Wrong pressure with rigid water

[Sudip Das]

Dear All,

I am simulating a protein in water with GROMOS96 force field (gromos54a7)
and SPC/E water model. After minimization followed by NVT equilibration, I
performed 2ns of NPT equilibration. From the converged box length I have
taken the average value and set the box length (in npt_equilibrium.gro
file) to that value and used this for NVT production run.

In the production run, temperature, potential and total energies are
reasonable, whereas the pressure is behaving weirdly. I have started the
NVT production run with 1 bar pressure.


NVT production run with flexible water (define = -DFLEXIBLE): P = 1 to 5 bar

NVT production run with rigid water: P = 750 to 780 bar


Did anyone encountered this kind of problem? I would appreciate your kind
help in resolving this.

Best regards,
Sudip