  The stability of a single-walled carbon nanotube placed on top of a catalytic
nickel nanoparticle is investigated by means of molecular dynamics simulations.
As a case study, we consider the $(12,0)$ nanotube consisting of 720 carbon
atoms and the icosahedral Ni$_{309}$ cluster. An explicit set of
constant-temperature simulations is performed in order to cover a broad
temperature range from 400 to 1200 K, at which a successful growth of carbon
nanotubes has been achieved experimentally by means of chemical vapor
deposition. The stability of the system depending on parameters of the involved
interatomic interactions is analyzed. It is demonstrated that different
scenarios of the nanotube dynamics atop the nanoparticle are possible depending
on the parameters of the Ni-C potential. When the interaction is weak the
nanotube is stable and resembles its highly symmetric structure, while an
increase of the interaction energy leads to the abrupt collapse of the nanotube
in the initial stage of simulation. In order to validate the parameters of the
Ni-C interaction utilized in the simulations, DFT calculations of the potential
energy surface for carbon-nickel compounds are performed. The calculated
dissociation energy of the Ni-C bond is in good agreement with the values,
which correspond to the case of a stable and not deformed nanotube simulated
within the MD approach.
