| Theoretical studies of nanoscale systems, such as functionalized carbon nanotubes (CNTs) and graphene, present major challenges to computational methods employed in quantum chemistry and condensed matter physics. For this reason, accurate numerical calculations for functionalized CNTs and graphene require a direct quantum mechanical approach. This thesis presents first principles calculations using density functional theory (DFT) to study the structural and electronic properties of functionalized and doped graphene and CNTs. The calculations are performed using density-functional pseudopotential computational methods combined with the generalized gradient approximation (GGA) for the exchange-correlation functional. The structural optimization of graphene and CNTs is carried out by energy and force minimization. We investigate the chemical functionalization of graphene and CNTs with carboxyl (COOH) groups. The binding energies, equilibrium geometries, and the charge transfer of graphene sheets and CNTs are examined. We find that the attachment of COOH groups induces substantial structural changes in graphene and CNTs. Our calculations show that the binding of the COOH group is significantly stronger in the presence of surface defects. The properties of graphene and CNTs doped with boron (B) and nitrogen (N) atoms are also studied. The calculations confirm that B doping increases and N doping decreases the binding energy of COOH groups to both defect-free and defective graphene and CNTs. The interactions between B and N atoms doping graphene are examined. The B-B and N-N interactions are found to be repulsive, while the B-N interaction is found to be attractive. |
