Dear usres Thank you for your replies
1- Is it possible define a ion as a propane molecule and then I do adding propane molecules instead of methane molecules in my system? 2- Other wise, I select 300 molecules of methane and remove them from my system(randomly and by hand, for example 500 molecules of methane and adding 100 molecules of propane,) [Dr. Vitaly Chaban comment] Is it possible and common method? I am using OPLS AA ff, Sincerely -- gmx-users mailing list gmx-users@gromacs.org http://lists.gromacs.org/mailman/listinfo/gmx-users * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/Search before posting! * Please don't post (un)subscribe requests to the list. Use the www interface or send it to gmx-users-requ...@gromacs.org. * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists