[lammps-users] limiting a group of atoms to translate as a unit


I’m running simulations (both MD and CG/SD) on a system of atoms subdivided into to two groups. I want to impose the constraint that all of the atoms in any of these groups undergo identical displacements, such that the two groups can only undergo translations as separate units. Note that this is different from making the groups into rigid bodies, because i want to allow translation only, not rotation.

To achieve the above, I’ve used the commands

fix 1 bot aveforce 0.0 0.0 0.0
fix 2 top aveforce 0.0 0.0 0.0

The input files in examples/flow use fix aveforce to do what you want.


Dear Mike,

Are the initial velocities of all the atoms same in a particular group???