[lammps-users] Carbon nanotube

I have some problems for modeling CNT. Would you please help me?

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.