hi,yang ye,I used the em.mdp you gave me before.It seemed like to have "none"there and worked well with other systems. Regards shanshan -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20070811/a5b1d163/attachment.html>