How to analyze tau-p / tau-t


I’m trying to understand how tau-p works and how to choose the right value.

I’m using GROMACS 2019, and the system is ice. Isotropic MD with Parrinello-Rhaman barostat with 1 fs timestep.

The graphic on the right tau-p is set 100 and the left one is set 2.

I appreciate If someone could explain the differences.

Thank you

Inna Nangoi and linked references goes through the theory of what tau is and what it does.

What it boils down to the lower the tau value, the faster the coupled parameter is pulled towards it’s reference value. It needs to be low enough such that the value doesn’t deviate away from the target value, but high enough so that it allows the system to respond to fluctuations not too harshly.

You can see this occurring with the two graphs you have shared, low value on left pulls the pressure (and hence volume) back towards the reference value quickly, high value on the is much slower.