[lammps-users] carbon nanotube simulation-please help

Hello all
I am doing simulations of CNTs.
1)I am trying to apply a force on a single atom of the carbon tube located around the center(of length). But could not do so, since the fix addforce command asks for a ‘group’ id whereas i want it for one atom. Is there a way to do it.
The group of atoms along the length(say bottom edge) are fixed and the force is applied on an atom belonging to top edge.

2) With the same conditions I applied forces on a group of atoms belonging to the top edge. I want to see at what value of force the bonds break. But in the simulation the bonds don’t break instead I could only see some vibratory motion. If I give huge values for force, then lammps gives me an error:Lost atoms
The code that I used:

units metal
boundary s s p
lattice hcp 1
atom_style atomic
read_data read8.cnt

pair_style airebo 2.5 1 1
pair_coeff * * CH.airebo C C C

group mobile type == 1
group fixed type == 2
group load type == 3

# Equilibrate
fix 1 mobile nvt 300.0 300.0 0.1
fix 4 load nvt 300.0 300.0 0.1
velocity fixed set 0.0 0.0 0.0
timestep 0.003
run 100



# Load
velocity fixed set 0.0 0.0 0.0
fix 3 load addforce 0.0 -1.0 0.0
dump mydump all atom 100 dump.cnt
run 10000



3)Also I want to simulate a situation where the same conditions exist but instead of applying a force on a single atom of top edge, a carbon atom from the surroundings at a certain velocity is made to collide with with that atom of CNT. Is this possible?

Regards
APC

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A group can be one atom.

Pushing atoms around is a tricky business b/c the forces
generated by atoms closely approaching each other are
very large. All of the things you describe are possible in
principle, you just need to be careful how you do it and monitor
the forces & thermodynamics and viz the results.

Steve