Dear Gromacs users , I have a xyz file and I used OBGMX ( topology generator ) for that . Now I have itp and top file , but the problem is I want to change UFF forcefield ( that used by obgmx ) to gromacs forcefields like Amber03 . Can you please let me know how can i do that ? I am new in Gromacs and i hope you can help me . Regards, Saeed.