Different configurations of a single nitrogen atom adsorbed at different sites on the sidewall of single-walled carbon nanotubes (SWNT's) are studied through first-principles calculations. It is found that the outer surface of the tube wall is reactive to the nitrogen atom, and a nitrogen atom can be chemically adsorbed on it forming an exohedral complex with a binding energy of; 3.86eV for a (5,5) SWNT. Although the inner surface of the tube wall is less reactive than the outer surface, a nitrogen atom can still be adsorbed on the inner wall of the (5,5) tube forming an endohedral complex with the binding energy on the order of ～1.78eV. The local structure of the SWNT around the adsorption sites is substantially changed. From studying the binding energies of a nitrogen atom adsorbed on different armchair tubes (n, n) with n ranging from 5 to 16, it is found that the binding energy for exohedral adsorption decreases significantly with increasing radius (or increasing n) of the tube, while for endohedral adsorption the binding energy varies slightly. The influence of endohedral adsorption of a single nitrogen atom on the local density of states of a (5,5) SWNT is also discussed.

The stopping power of slow antiparticles penetrating electron gases are evaluated within a scattering theory approach to the energy-loss problem. The required effective scattering potential is obtained from a selfconsistent density-functional calculation. A relationship of the stopping power Sα|Z|b (b is in the range of 0.7-0.9) at low velocities is found, in contrast to the Z2 dependence predicted by the linear-response theory. The diffuse distribution of partial wave contributions of screening electrons in the case of antiparticles is quite different from that for normal particles and is thought to be the main reason for the monotonic increment of the stopping power as a function of |Z|.

A model of an ion embedded in jellium is presented. The static charge state of a heavy ion is determined self-consistently. The effective charge of a heavy ion at low velocities is calculated, which is incorporated with the Brandt-Kitagawa effective charge theory to take the velocity dependence of the effective charge into account. The quantal harmonic oscillator model is generalized to calculate the electronic energy loss of heavy ions colliding with a carbon target. The results are compared with available experimental data.

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.

The growth process of higher fullerenes through adduction of small carbon clusters and carbon atoms is studied using a molecular-dynamics simulation method. Small clusters, such as C3 and C2, and carbon atoms easily adsorb on the surface of fullerene cages, which have coordination-number defects or topological defects, when they collide at thermal velocities with the fullerenes. Annealing the chemisorption complexes at 3000K, the attached clusters are soon incorporated into the network of the fullerene cages, via a self-assembly growth process. Although the fullerenes grown in this way usually have defects, their ring structures can be described by a formula deduced from Euler's theorem. The energies of the fullerenes remarkably decrease with their increasing size, when they are annealed to their low-lying energy structures.