I'm afraid I don't have an answer for you but maybe I can point you towards better help. If you're doing MD in gromacs then I'm guessing you're either a physicist or a theoretical chemist. This is a general linux OS discussion board so there probably aren't a lot of people here who know anything about gromacs. I'm a theoretical physicist, but I don't use gromacs so I'm no help to you. You really want a gromacs-specific discussion group. Try:
or see if any of your peers know a better place for gromacs discussion.