[gmx-users] Thin film drifting

[Alex]

Dear all,
In a system, I have a thin_film (infinitive in x-y directions) with water
on top and bottom of it, PBC = xyz.
By the below flags I try to remove the motion of the center of mass of the
two group separately.
comm-grps     = thin_film Water
comm-mode   = Linear
nstcomm         = 100

However the thin film drift specially in x and y directions whereas I was
expecting to have no drifting for the thin film, If I understood correctly
the usage of the comm-grps!

Would you please let me know how I can stop drifting of the thin film?

Thank you,
Alex