The hydrogen-storage behavior of single-wall carbon nanotubes was studied using molecular dynamics simulations and ab initio electronic calculations. Hydrogen atoms with kinetic energy of 16-25eV were observed to penetrate into and be trapped inside the tube. Consecutively injected H atoms form hydrogen molecules, and gradually condense to become liquid hydrogen in the tube. The density of injected hydrogen in the tube and the pressure on the wall of the nanotube induced by the stored hydrogen molecules were evaluated at room temperature.

Molecular-dynamics simulations were used to investigate the storage capacity of hydrogen in single-walled carbon nanotubes (SWNT's) and the strain of nanotube under the interactions between the stored hydrogen molecules and the SWNT. The storage capacities inside SWNT's increase with the increase of tube diameters. For a SWNT with diameter less than 20 ?, the storage capacity depends strongly on the helicity of a the SWNT. The maximal radial strain of SWNT is in the range of 11%-18%, and depends on the helicity of the SWNT. The maximal strain of armchair SWNT's is less than that of zigzag SWNT's. The tensile strengths of SWNT's decrease with increasing diameters, and approach that of graphite (20 GPa) for larger-diameter tubes.

Collisions between two C60 molecules are studied using molecular dynamics simulations. The results show that dumbbell-shaped (C60)2 dimers with almost intact cages can be formed at low collision energies, and when the collision energy is high enough to overcome the fusion barrier, the two colliding C60 molecules fuse to form one large C120 cluster. These coalescence reactions are found to have very clear threshold behavior. The threshold energy of dimerization is dependent on the classical impact parameter between the mass centers of the colliding partners, and on the collisional orientation. The coalescence reactions are shown to be deep inelastic. The total cross section for the coalescence reaction is estimated to be on the order of the area of a circle, that has a radius equal to the diameter of a C60 molecule.

The growth of narrow single-wall carbon nanotubes through adduction of small carbon clusters is studied using a molecular-dynamics simulation method. Statistical behavior of the growth and defect formation process is analyzed. For C2 dimer colliding onto the side-wall of narrow single-wall nanotubes, it is very easy to get the dimer to be incorporated into the network of the tube during annealing, forming localized topological defects. During long-time annealing at 2300K, thermal fluctuation can cause structural switching among different metastable states and thereby result in energy pulses in the energy vs time curve.

Defect structures of fullerenes and fullerenelike clusters produced by two C60 molecules colliding at different impact parameters and different collision directions in the energy range 50-600eV have been studied using a molecular-dynamics simulation method. The electronic structures around the defects are obtained using a self-consistent-field Hartree-Fock scheme. The results show that the numbers of coordination-number defects obey a magic rule, and the numbers of rings forming the closed cage structure of the fullerene or fullerenelike products can be well described by a modified formula deduced from Euler's theorem. The electronic structures around the defects are substantially changed in comparison with those of the carbon atoms on normal fullerene cages.