fix npt - pressure not equilibrating

Hi Users,

I’m using an NPT ensemble to set the pressure of the simulation at 1 atm, however, when I run the simulation the pressure is not relaxing to 1 atm (it’s actually in the negative). My settings are:

units real
timestep 1.0
fix 1 all npt temp 300.0 300.0 100.0 iso 1.0 1.0 1000.0

The first question is, am I setting the NPT fix correctly? If that is correct, then, could I be setting the Pdamp incorrectly?

Any help would be appreciated.

Thanks,
Casey

Hi Users,
I'm using an NPT ensemble to set the pressure of the simulation at 1 atm,

how long is your trajectory and how far are you away from equilibrium?

however, when I run the simulation the pressure is not relaxing to 1 atm
(it's actually in the negative). My settings are:
units real
timestep 1.0
fix 1 all npt temp 300.0 300.0 100.0 iso 1.0 1.0 1000.0
The first question is, am I setting the NPT fix correctly? If that is

looks correct. remember this is defining a relaxation time of 1 picosecond.

correct, then, could I be setting the Pdamp incorrectly?

you can play a little with making Pdamp shorter, but if you make
it too short, it will result in bad dynamics. pressure relaxation
can be tricky and may need time and some experimentation.

if you know that your system is going to shrink, you could
start by initially shrinking the box and rescaling the atom
coordinates accordingly with displace_box and then run some
minimization steps to reduce the resulting high potential energy
before switching to npt. that may help to speed up the process.

cheers,
    axel.