Dear GROMACS Users: I would like to use the g_tcaf command to compute the viscosity of ionic liquid. I found out (searched online) that the g_tcaf command has some problems. I used the following command g_tcaf -f traj.trr -s NPT.tpr -n index.ndx -oa tcaf.xvg But got error messages. Does anybody know how to fix this problem? Thanks! Andy