Hello, I am doing solvation dynamics for my system. When I am running grompp command I get the error. grompp -f md.mdp -c solvent-bmi-pf6-128.pdb -p solvent-bmi-pf6-128.top -o md-rerun.tpr Fatal error: No such combination rule 0 I using Gromacs VERSION 4.0.5. What this error means? Thanks NIlesh