[gmx-users] how to generate a *.mdp file?

[Maria Sabaye Moghaddam]

Hello;

	I am very new with gromacs.  I am at the initial stages of getting 
a trihelix in water simulation going.  I have generated the *.gro and
*.top files, but I don't know how to generate an *.mdp file.  I copied the 
one from the "Getting Started" section, but I am getting error messages
like:
filename_A.itp : No such file or directory
filename_B.itp : "  "    "     "  "

and then 

Fatal error: No such moleculetype Protein_A

Can anyone help me with this please?

Thanks,
Maria.