Fix Setforce issue

Dear all,

I simulated a system that includes some water molecules and also one cubic nanodiamond. I would like to fix the nanodiamond in its place and don’t let it to move or rotate. So, I applied fix setforce 0 0 0 and velocity 0 0 0 commands on three atoms of nanodiamond. But in this situation, the water molecules collapse and leads to some regions of the simulation box to become empty. This does in both of NVT and NPT ensembles. without fix setforce the simulation works fine.

Thanks a lot,

Three comments:

  • if you did correctly what you say you did, then this will not have the effect you describe. So there must be something done incorrectly
  • it is much simpler to immobilize atoms by not including them in the group that the time integration is applied.
  • if you want to retain a group of atoms near a specific position and inhibit rotation, while they still can move and have a temperature, you need to use fix spring/self