Open nvt.xtc you will see water molecules filing larger than initial space. In my opinion that is wrong or at least I do not want that. -- View this message in context: http://gromacs.5086.x6.nabble.com/My-box-size-canges-somehow-tp5015721p5015734.html Sent from the GROMACS Users Forum mailing list archive at Nabble.com.