The interaction of atoms, molecules, and clusters with graphite and metal surfaces.

摘要

Self-Consistent Field Linear Combination of Atomic Orbitals - Molecular Orbital (LCAO-MO) method has been used to study the interaction of atoms, small molecules, and small atomic clusters with surfaces of metals and graphite. The bulk metal surface and graphite have been represented by a limited collection of atoms placed at the bulk lattice sites. The effect of the limited size of the bulk surface has been eliminated through suitable treatment of the end atoms. The studies have yielded information on the electronic structure, bonding characteristics, and magnetic behavior of the atoms, molecules, and clusters due to the interaction with the surfaces. The calculations have been performed through the Hartree-Fock approximation with correlation correction or density functional theory with generalized gradient correction. The studies include the interaction of H₂ with copper and nickel surfaces, Li₃ cluster with lithium metal, Li and H atom and H₂ molecule with graphite surface. On the metal surfaces the H₂ molecule stabilized in a physisorbed position before passing over an activation barrier to end up in dissociative chemisorption on the metal surface. The Li ₃ cluster interacted strongly with the Li metal surface and atoms of the cluster lost their identity and became an integral part of the metal bulk surface. A Li atom interacting with graphite preferred to bind above the center of a carbon ring. However, it preferred to go between the layers of graphite with a much stronger binding similar to intercalation of Li in graphite. H and H₂ did not bind with a pristine graphite surface, an observation borne out by experiments. Since interesting experiment and theory exist on deposition of transition metal atoms on benzene and coronene molecules, another similar molecule, pyrene was studied for deposition of Fe atoms. It could bind four iron atoms, one for each carbon ring. Moreover, these iron atoms coupled ferromagnetically. This can have possible implications in industry. The final study involved the interaction of a hydrogen atom with the inside surfaces of a vacant site in bulk aluminum metal. It was observed that the hydrogen atom went off-center to interact with aluminum atoms at a distance similar to the Al-H distance in the dimer. This explains experimental observations in bulk aluminum.