[gmx-users] Error in energy groups

[masoud keramati]

Hi all

i have a protein with six chain.
i create an index file that include each chain (chA chB ..)
in mdp file i define energy groups such that:
energygrps   = chA chD

for grompp i used this command:
gmx grompp -f md.mdp -c npt.gro -n chains.ndx -p topol.top -o A-D.tpr

but i got this error:
"Group Non-Protein referenced in the .mdp file was not found in the index
file.
Group names must match either [moleculetype] names or custom index group
names, in which case you must supply an index file to the '-n' option
of grompp "

what's wrong with this?!

thank for your help : )