Thesis (Ph. D.)--Washington State University, December 2009. / Title from PDF title page (viewed on Dec. 11, 2009). "Department of Physics and Astronomy." Includes bibliographical references (p. 156-176).

In this dissertation, we have employed some well-established electronic-structure methods [e.g., density functional theory (DFT) and time-dependent DFT (TD-DFT)] to investigate the potential energy surfaces for 2s 2p excitation of beryllium atomic clusters, attempting to provide direct computational support for the mechanism of a newly invented laser spectroscopy. The computing time of single-point energy calculations for a series of beryllium clusters from using TD-DFT has been compared with that from a higher-level coupled-cluster method, in order to demonstrate the computational practicality of TD-DFT methods. Meanwhile, to benchmark the accuracy of TD-DFT methods, the state properties such as the equilibrium inter-atomic distance and dissociation energy of beryllium clusters calculated by us are compared with experimental results and other computational values where available. Furthermore, we have defined the fork intersections to characterize the position where the excited states can be treated as degenerate = Moreover, to shed some light on the reaction mechanism of a Diels-Alder reaction between isoprene and maleic anhydride, we have investigated the kinetic isotope effects (KIE) of the reaction. To further include inter-nuclear quantum-statistical effects (i.e., the quantum tunneling effect and anharmonicity), an automated integration-free path-integral (AIF-PI) method developed by our group in recent years based on Kleinert's variational perturbation theory has been used. The KIE values produced by the AIF-PI method can be used to clearly distinguish between the two isomeric transition-state structures, and determine the actual rate-limiting transition state. By virtue of the AIF-PI method, we have also analyzed the quantum tunneling effects and anharmonicity separately, which are excluded in conventional Bigeleisen equation. Furthermore, the influence of different numbers of quantized nuclei on the KIE values using base-catalyzed RNA 2'-O-transphosphorylation models as examples are explored, by systematically increasing the number of quantized nuclei from 1 to 16 (fully quantized)

Graduation date: 1997

published_or_final_version / Physics / Master / Master of Philosophy

Thesis (Ph.D.)--Auburn University, 2007. / Abstract. Vita. Includes bibliographic references (ℓ. 150-163)

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 68-69).

Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2010. / Committee Chair: de Heer, Walter; Committee Member: Chou, Mei-Yin; Committee Member: First, Phillip; Committee Member: Whetten, Robert; Committee Member: Zangwill, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--Washington State University, May 2007. / Includes bibliographical references (p. 234-257).

This thesis explores the synthesis, properties, and potential applications of molecular clusters and the hierarchical solids that form when complementary clusters are combined. Chapter 1 introduces the diverse set of molecular clusters that I employ as nanoscale building blocks in the assembly of multifunctional materials. The core structure of the molecular clusters is closely related to the superconducting Chevrel phases. In discrete clusters, however, the core is passivated by organic ligands, which add stability and important functionalities. The molecular clusters have rich physical and chemical properties of their own, and I present some of the techniques used to investigate their intrinsic electronic properties. Finally, I review some of the modes by which the molecular clusters interact with another to assemble into hierarchical solids. The structural tunability and complexity embedded in the molecular clusters will enable the design of modular, well-defined, multifunctional materials with desirable electronic and magnetic properties. Chapter 2 details the synthesis and characterization of a family of manganese telluride molecular clusters. By varying the ligands that decorate the surface of the inorganic core, I show that the core structures can be tuned. The study of molecular clusters provides insight into how extended solids form. As such, I make structural comparisons of the clusters to known solid-state compounds. Being structurally varied and chemically flexible, the clusters reported in this chapter present an exciting new class of building blocks for the assembly of solid-state compounds. In Chapters 3-4, I present a nanoscale approach to investigate the electronic behaviors of individual molecular clusters. By using a scanning tunneling microscope-based break-junction technique and density-functional theory calculations, I study the effects of the junction environment and the redox properties of the molecular clusters on the conductance of single-cluster junction. Importantly, current blockade effect is observed at room temperature in the single-cluster junctions, allowing for the conductance to be turned on or off by varying the bias potential. Chapters 5-7 explore the synthesis and properties of the hierarchical solids comprised of molecular cluster building blocks. Chapter 5 unveils an approach to create a three-dimensional (3D) coordination network of molecular clusters by using a bifunctional cyanide ligand. The cyanide ligand is appended to the metal sites of the cluster through the carbon terminus, leaving the nitrogen end available for coordination by a divalent metal cation. Whereas the molecular cluster itself is paramagnetic across a temperature range of 3-300 K, the 3D coordination compound shows a ferromagnetic transition at ~25 K. In Chapter 6, I describe the importance of a molecular recognition feature on the molecular cluster that contributes to the assembly of a layered, van der Waals solid. The bulk material contains monolayers of fullerene and can be mechanically exfoliated to thinner layers, providing a key templated strategy to isolate free monolayers of fullerene. Lastly, Chapter 7 details layered, van der Waals solids of rhenium and molybdenum synthesized using traditional solid-state reactions. Because the neighboring cluster units are covalently bound together, the inter-cluster coupling is much stronger in the plane of these materials than that of the self-assembled solid described in Chapter 6. The strong two-dimensional (2D) character in these layered materials allows for the exfoliation of bulk crystals into robust, low-defect monolayers. The surfaces of these monolayers are covered with substitutionally labile ligands, which is an atypical yet valuable feature among 2D materials. I demonstrate that the electronic properties of the monolayers can be tuned by exchanging the surface ligands.

This dissertation describes and summarizes the research I performed as a member of the Roy group. The Roy group uses molecular clusters as nanoscale building blocks for new materials, in addition to several other topics of related interest including the design and synthesis of molecular wires to study the movement of electrons (conductance) at the molecular level. Chapter 1 introduces molecular clusters as superatomic nanoscale building blocks and describes how superatomic crystals, analogous to ionic crystals, can be controllably assembled from these building blocks. Next, Chapter 2 examines how the atomic properties of ionization energy and electron affinity can be extended to superatoms by investigating the Co6S8(PEt3)6(CO)6-x family of clusters. As the degree of cabonylation increases, the superatom moves from alkali-like to halogen-like behavior; i.e., it becomes harder to ionize and easier to add an electron to the superatom as PEt3 ligands are replaced with CO ligands while still maintaining the overall electron count of the cluster. Chapter 3 then moves to discuss how the related building blocks, Co6Te8(PEt3)6 and its derivatives, can be assembled into superatomic crystals using the electron-accepting Fe8O4pz12Cl4 cluster. Chapter 4 then uses this same Fe8O4pz12Cl4 cluster as a probe for singlet fission triplet dynamics by functionalizing this cluster with a singlet fission chromophore. Chapter 5 continues the idea of ligand design by exploring a series of oligophenylenediamine molecules capable of binding to gold (and presumably other metals), and it is observed that the conductance dramatically increases by applying a high positive bias to the molecules when they are bound to the tips of two gold electrodes. This dissertation concludes with Chapter 6, which discusses how new cobalt chalcogenide materials prepared from superatomic precursors can be deployed as new battery electrode materials for lithium and sodium ion batteries. Each of these chapters help illustrate how synthetic chemistry can be used to both elucidate interesting chemical phenomena and to design new materials with tailored properties.