Dear Mark thanks for your attention when I used trjconv -pbc nojump, I made one group (protein and dna) in index file and I selected that as centering group. -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://maillist.sys.kth.se/pipermail/gromacs.org_gmx-users/attachments/20101020/35b3828a/attachment.html>