How can I find the appropriate NVT/NPT equilibration time

GROMACS version: 2019.4
GROMACS modification: Yes

I’ve tried to simulate Umbrella Sampling on the DOPC bilayer system and I wonder how long I simulate the NVT/NPT step for the correct orientation on the system.

It takes so long time when I run the equilibration step over 50ns but in contrast, if I simulated the equilibration step during 200ps, it it too short to consider the system stable.

I want to know how to find whether the system is in the equilibration with the correct orientation ‘during appropriate time’

That entirely depends on what property you are looking for to stablise and are interested in.

If the property you are studying equilibrates over 100s of ns, then you need to run for at least that time frame to be sure that it has equilibrated. If it is say density, then it may equilibrate over nanoseconds, so that is all you need to run it for.

How is it that you measure the “orientation”? Have you monitored it with time to see how it has changed?

That I measure the ‘orientation’ just means whether the system interested in is in stable equilibration state.

And I used to monitoring with vmd