I’m trying to use lammps to study material annealing, and in my study process, I want to fix some groups but not ‘fix group’ command, because I want them to do the whole movement. so I want to use ’ fix shake ‘command. In the manual, it said ’ LAMMPS allows for the following kinds of clusters to be constrained: one central atom bonded to 1 or 2 or 3 atoms, or one central atom bonded to 2 others and the angle between the 3 atoms also constrained’. But my clusters have five toms, for example phosphate ( PO4 ), so I don’t know how to 'fix shake ’ the clusters. Do you have some suggestions? And I’m very glad for you response. Thank you very much!