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Reverse nonequilibrium molecular dynamics (RNEMD) is employed to study the phononic thermal transport properties of C3N nanotubes. We study the effect of nanotube length and diameter on the thermal conductivity and investigate the phonon transport transition from ballistic to diffusive regime in C3N nanotubes. It is found that the thermal conductivity of C3N nanotubes is significantly lower than those of carbon nanotubes across the entire ballistic-diffusive range. In addition, significantly lower ballistic to diffusive transition length (72–80 nm) is observed in C3N nanotubes compared to carbon nanotubes. The inspection of phonon dispersion curves shows that carbon nanotubes have stiffer acoustic modes than C3N nanotubes which results in lower group velocities for C3N nanotubes. Due to the presence of nitrogen atoms, the phonon mean free paths and relaxation times of C3N nanotubes are shorter than those of the carbon nanotubes. The combined effect of lower group velocities and relaxation times leads to the lower thermal conductivity of C3N nanotubes.

The impact of hydrogenation on the fracture toughness and strength of grain boundaries in graphene are studied. Molecular dynamics (MD) modeling is used to extract the traction−separation laws of two high-angle symmetric grain boundaries. The MD modelings are conducted on two bicrystalline graphene sheets, while their grain boundaries are hydrogenated. The impacts of the adsorption site of the hydrogen atom, hydrogenation percentage, and temperature are studied. The results show that in general the hydrogenation of the grain boundaries leads to a reduction in both their strength and ductility. The adsorption site is an important factor for determining the level of the impact of hydrogenation on the fracture properties of the grain boundary. An increase in the temperature from 1 to 300 K reduces the strength of hydrogenated grain boundaries, whereas toughness increases initially and then decreases.