How can I apply a flux to molecules?

GROMACS version: 2016.4
GROMACS modification: No

Hi all,

I’m working with an infinitely long channel filled with water. I’d like to apply an acceleration to the water molecules and measure the subsequent flux. I’m quite confused about how exactly to do this, does GROMACS have a feature to easily apply a constant force to the molecules and measure the flux (or is the flux something I would write an external code for?)?

Thanks in advance

you can have a look at the acc-grp opinion in mdp parameter