[lammps-users] why there is no interaction?

Hi ,
i am trying to simulate a simple interaction between one site CO2 and a simple SWNT assuming to be rigid just for now. I am running the simulkation,after a minimization, and then i am trying to visualize it.I see that there is no interaction between the C atoms of carbon nanotube and the CO2 molecules. Why is this happening?What am i doing wrong?

dimension 3
boundary p p p
units real
atom_style molecular
neighbor 0.3 bin
neigh_modify delay 5 every 1

read_restart co2min-Rav-swnt.restart

# Type 2: Carbon atoms
# Type 1: CO2 atoms
group CO2 type 1
group tubes type 2

pair_style lj/cut 20.0
pair_coeff 1 1 0.468781 3.454 10.0 #CO2-CO2 epsilon(kcal/mol) sigma(A)
pair_coeff 2 2 0.0 3.0 0.0 #C*-C*
pair_coeff 1 2 0.557 3.40 20.0 # CO2-C*

# the tubes are frozen
fix 1 tubes rigid single
fix 3 tubes setforce 0.0 0.0 0.0
fix 4 CO2 npt temp 300 300 100 iso 1.0 1.0 1000.0
thermo 200
log produc.log
thermo_style custom etotal ke temp pe ebond eangle press vol
thermo_modify line multi
timestep 1.0
dump 1 all atom 500 Rav-swnt.lammpstrj
dump_modify 1 image yes
run 500000

write_restart Rav-swnt.restart

how do you know there is no interaction? Did you print out that information? Try compute group/group command to calculate interaction between two groups and see if is zero.

I haven't done that. I visualize my results just to have a first look about what am i doing.And i saw that there is no CO2 molecule near the nanotube.