I ran the simulation for water transporting through aquaporin protein for about 500ns. I got the .xtc file and .gro topology file . Then I calculated the waters that are permeating through aquaporin protein . I want to calculate the osmotic permeability that is "pf" of these waters for this channel . The protocol for calculation based on the collective diffusion model proposed by Zhu et al. I am not able to get how I can do this . Can Someone help me in this regard.