Thesis (M.Sc.)--Chulalongkorn University, 1996

The quantum chemical study of the Li-C60 complexes was carried out using ab initio UHF calculations with the 6-31G basis set. The electron distribution on the surface of C60 and the change of dipole moment of the complexes when the lithium atom approaches perpendicularly to the surface in different trajectories have been investigated. It was found that the most stable trajectory is that perpendicular to the center of the hexagon (C6). In addition, potential functions for both endohedral Li@C60 and exohedral LiC60 complexes have been separately developed. Calculations also have been carried out for the exohedral LinC60 complexes, where n=1-6 and 12 using the STO-3G and the 6-31G basis sets. The results obtained from both basis sets were in good agreements, in which the electron donated by the lithium atom leads to deformation of the geometry of C60. Furthermore, electronic structures and molecular orbitals of these complexes have been analyzed in order to explain the conductivity characteristics of the system. It was found that Li3C60 displayed lowest HOMO-LUMO energy gap, and hence showed highest conductivity. However, the calculated energy gap indicates that the investigated system is an insulator. Besides, the threshold energy of collision for firing lithium atom to penetrate through the surface of C60 has been computed and found that the penetration via the trajectory C6 requires lowest energy of approximately 28 eV