GROMACS MLより

You might want to consider OPLS-AA 2005 as implemented in the Shorodinger software. The Schrodinger Maestro is FREE for academia, after registering you can download it and use. There is an utility "ffld_server", which is able to automatically assign OPLS-AA 2005 to any ligand molecule. Once you have the output of ffld_server, you can convert this into gromacs topology format by a python program called "ffconv.py" (see? http://frolov-pchem.wikispaces.com/Downloads ). Also you can check if the conversion in your case was correct by "check_conversion.sh" script therein. This is well-documented and has real-life examples, so it is easy to start using this. See the documentation inside.