[lammps-users] Carbon nanotube

Many thanks for your answers.

1-What should I do to put only a displacement constraint as a boundary
condition on a CNT?
2-If we do not have any bonds in AIREBO, then how can I know the amount of
stress in a bond? Should I change my potential function?
3-Imagine a CNT that I have replaced one Hydrogen atom instesd of one Carbon
atom with an AIREBO potential function. Now, I time integrate the nanotube.
In the output, I see that the Hydrogen atom (or even atoms) do not have any
displacement and all the velocity components are zero.
The same thing happened for a CNT and a SI atom with TERSOFF potential
function. Is there anything wrong here?
4-I want to model a CNT under tension.

units metal
boundary s s p
lattice hcp 1
atom_style atomic
read_data swnt.txt
pair_style airebo 3.0 1 1
pair_coeff * * CH.airebo C C C H
group mobile type == 1
group load type == 2
group fixed type == 3

fix 3 load addforce 0.0 -0.0 -1.0
fix 1 mobile nvt 300.0 50.0 0.001
fix 4 load nvt 300.0 50.0 0.001
fix_modify 3 energy yes
fix_modify 1 energy yes

timestep 0.001
thermo 50
compute 1 all displace/atom
compute 2 all stress/atom
#displace_atoms fixed move 0 0 0 units box
thermo_style custom step temp pe ke etotal epair
dump mydump all custom 10 dump-cnt4.txt id type mass xs ys zs vx
vy vz fx fy fz c_1[1] c_1[2] c_1[3] c_1[4] c_2[1] c_2[2] c_2[3]
run 1500

5-Is there any site which can help me to model SW defect?
Do you have any samples that can help me?

Best regards

AIREBO does tally the per-atom stress on each atom,
which you can output. To debug your problems,
I suggest you output forces and velocities of individual
atoms (dump custom) and see which ones, if any, are zero.