Energy partitioning within a one-electron formalism: Theory and applications to small molecule chemisorption on metallic surfaces.

摘要

Chapters 1 and 2 of this dissertation focus on the formulation of Hamilton population analysis---a scheme for partitioning the total energy of molecular and extended materials in one, two, and three dimensions---within a semi-empirical extended Huckel framework.; In chapter 1 the characteristics of Hamilton population analysis are contrasted with those of Mulliken's overlap population analysis. Mulliken's overlap population analysis---a partitioning of the valence electron density amongst the atoms and bonds---results in atomic charges and bond populations that have long proven their worth in qualitative studies of chemical bonding in both molecules and solids.; The molecular Hamilton population formalism introduced in chapter 1 is extended in chapter 2 to treat bonding in one, two, and three dimensional materials. A variety of energy partitioning schemes based on both valence and fragment orbital basis sets are presented.; Chapter 3 deals with the application of the Hamilton population formalism to the study of CO chemisorption on the Ni(100) surface. The Hamilton population formalism effectively highlights significant surface-CO bonding contributions from low-lying (non-frontier) CO molecular orbitals and the surface s and p bands. The inclusion of such contributions in surface-CO bonding models represents a significant extension of traditional, frontier-orbital based models of surface-CO bonding.; Chapter 3 concludes with a comparative energy partitioning study of Ni-CO bonding in the c(2 x 2)-CO/Ni(100) chemisorption system and a "molecular model" of the surface chemisorption site.; The model of surface-CO bonding proposed in chapter 3 is extended in chapter 4 to include CO chemisorption on the Pt(111), Cu(111), and Al(111) surfaces. By choosing to study CO chemisorption on both transition metal and main-group surfaces the role of the surface d-band in binding CO to the surface can be fully investigated.; The formation of the surface-CO chemisorption bond is interpreted as the net result of variations in surface-CO, C-O and M-M (M = Pt,Cu,Al) bonding.; In the final chapter Hamilton population analysis is used to investigate the changes in electronic structure accompanying the reaction between coadsorbed CO and O on the Pt(111) surface. A surface-mediated co-activation of CO and O is proposed to account for the reaction barrier and the roles of the individual CO and O orbitals in OC-O bond formation are discussed.