This thesis is composed of three parts. Part I describes a DFT study of the C60 dimer cations and anions which indicates that [2+2] isomers are lower in energy than single bond (SB) isomers. The center to center distances (CCD) of these two isomers calculated in our study are in fair agreement with experiment. Part II presents a good model (Fe+-oronene) and a scheme to simulate the binding of iron cations to [n, n] nanotubes. The binding energy from all DFT calculations increases as the nanotube diameter decreases, which can be explained by pi-orbital axis vector (POAV) theory. LSDA and PW91PW91 are believed to overestimate the binding energy while BPW91 and B3LYP are expected to give better results. Part III analyzes two possible patterns of fluorine addition to single wall carbon nanotube that have been proposed as 1,2 and 1,4 addition. Semi-empirical calculations indicate that the 1,4 isomer is lower in energy. Fluorine atoms prefer to grow along the tube for the 1,2 isomer whereas for the 1,4 isomer, they prefer to grow around the tube. This is consistent with results from a STM study of the fluorinated nanotubes.