[lammps-users] freezing atoms

Dear lammps users,

I have a problem in freezing a group of atoms in my simulation. I used the command
fix setforce 0.0 0.0 0.0. But when I use this command I get the van der wall energies
positive. One more way i tried is that i did not include that group of atoms in the
integration. So basically they won’t move. But I am not sure whether the interaction
between these atoms and other group of atoms will be included in the claulation of
total energy. Can any one please help me out in freezing a group of atoms in my simulation. Thank you in advance…


Using a fix to set their force to 0 or not integrate them will
not change the fact that their energy of interaction is included
in thermodyanmic output (although it should just be a constant).

If you want their energy to disappear you could:

exclude their pairwise interactions (neigh_modify exclude type)
  if they are a different type
sum up per-atom energy (compute pe/atom and compute reduce)
  for all atoms except those