  Recently, TersoffCG, a coarse grain potential for graphene based on Tersoff
potential, has been developed. In this work, we explore this potential,
applying it to the case study of a single wall carbon nanotube. We performed a
series of molecular dynamics simulations of longitudinal tension and
compression on armchair carbon nanotubes, comparing two full atomistic models,
described by means Tersoff and AIREBO potentials, and the coarse grained model
described by means of TersoffCG. We followed each stage and mode of
deformation, finding a good matching between the stress strain curves under
tension independently from the used potential, with a small difference in the
pre-fracture zone. Conversely, under compression the coarse grain model
presents a buckling stress almost the double of the full atomistic models, and
a more than double post-buckling stress. With the increase of the nanotube
diameter, the capturing of the buckling modes is enhanced, however the stress
overestimation remains. A decreasing of the three body angular term in the
potential can be a rough way to recover the buckling stress, with small losses
in the capturing of the post-buckling behavior. In spite of a good agreement
under compression, the fracture behavior of the nanotube is strongly
influenced, suggesting this modification only when no fractures are present.
The findings reported in this work underlie the necessity of accurately
evaluate the use of a coarse grain model when compressive loads are applied to
the system during the simulation.
