Comparison of quantum chemical surface modeling methods and theoretical study of self-assembled monolayer systems

Abstract

The detailed characterization of surface is not only of fundamental importance but also of interest for many applications. Using the quantum chemical calculations, a detailed knowledge of surface chemistry can be obtained at a molecular level. Research work in this thesis covers both popular quantum chemical surface modeling methods cluster and slab. The geometric and electronic structures of small mercury clusters, $Hg_n$, $Hg_n^{+}$, and $Hg_n{-}$ (n $\leg$ 8) have been calculated using a density functional theory (DFT). The results indicate that as the cluster size increases, the lowest energy states of neutral and anionic mercury clusters prefer three-dimensional structure whereas those of cationic clusters are peculiarly linear structure due to $\It{s-p}$ hybridization. This structural feature has influence on the energetic and electronic properties of cationic clusters which deviate from the characteristics of van der Waals cluster. As the cluster size increases, energetic properties, binding energies per atom and second order difference in total energy of cationic clusters consistently decrease, in contrast to the neutral and anionic clusters. However, neutral and charged mercury clusters show common features in terms of size dependent transition of bonding character, such as the decrease of band gap and vertical ionization potential, and the increase of vertical electron affinity. These various properties are also qualitatively and quantitatively in line with the available experimental and theoretical results, implying the reliability of the ground state geometries of these clusters. Quantum chemical calculations of the reconstruction structures of Ge(001) surface were performed using DFT method. Using both slab and cluster models, we have systematically investigated the proper simulation models which show good accordance with experimental structure factors of surface dimers. From this analysis, more than 8 layer slab and two-dimer cluster models ar...