can you write the atoms 6002 6004 6006 6017 6021 and all informations in your topology file about these atoms?? Francesca -- View this message in context: http://gromacs.5086.n6.nabble.com/One-molculetype-for-3-proteins-tp4997727p4997758.html Sent from the GROMACS Users Forum mailing list archive at Nabble.com.