CHARMM Development Project Forums User Discussion & Questions Parameter Set Discussion Charmm General Force Field (CGenFF) download link

Another note: please never use CGenFF for biological macromolecules!!!
The Protein, Nucleic Acid, Carbohydrate and Lipid force fields are highly optimized for their specific purpose. The general force field is designed to cover any combination of chemical groups. This inevitably comes with a decrease in accuracy for representing any particular subclass of molecules, such as proteins, nucleic acids, carbohydrates and lipids. It is for this reason that we removed the amino acids, nucleotides,... from CGenFF. If you re-introduce them, you will waste a lot of time and obtain bad results.

Here is what you should do instead:

1. Make an "ATOM" section in the protein/nucleic acid/carbohydrate/lipid parameter file, containing all the MASS entries from the corresponding topology file. A sample protein parameter file can be found in the tutorial on the MacKerell lab website.
2. Renumber all "ATOM" fields in the CGenFF topology and parameter files so that they don't coincide with the protein/nucleic acid/carbohydrate/lipid atom numbers. The tutorial contains a script do_remas that does this for you.
3. read in the resulting topology and parameter files as follows:

   
   open unit 10 read form name @TOPPAR/top_all22_prot.rtf
   read rtf card unit 10
   close unit 10
   open unit 10 read form name @TOPPAR/par_all22_prot.prm
   read param card flex unit 10
   close unit 10
   open unit 10 read card name @TOPPAR/top_all36_cgenff_remas.rtf
   read rtf card unit 10 append
   close unit 10
   open unit 10 read card name @TOPPAR/par_all36_cgenff_remas.prm
   read para card flex unit 10 append
   close unit 10