Saudi Cultural Missions Theses & Dissertations
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Item Restricted Understanding 2D Elemental Ferroelectrics(University of Cambridge, 2024) Altowaijri, Loay; Artacho, EmilioFerroelectricity, traditionally found in compound materials composed of multiple elements, has now been observed in elemental monolayers of group-V element (Bi) with buckled lattice structures similar to phosphorene. Through first-principles calculations, this study reveals spontaneous electric polarization and ferroelectricity in antimony 2D material, antimonene. The polarization was driven by spontaneous lattice distortions and atomic layer buckling as a consequence of weak sp3 orbital hybridization that breaks inversion-symmetry-breaking making an in-plane polarization. This work, broadens the understanding of ferroelectric mechanisms in group V elements and hope it would spark this line of research for future studies and potential applications in next-generation electronic and optical devices, emphasizing the unique properties and versatility of 2D elemental ferroelectrics.10 0Item Restricted ADVANCING THE TREATMENT OF RELATIVISTIC THEORY WITHIN THE OLCAO PACKAGE AND WITH APPLICATION TO SOLAR PHOTOVOLTAIC TECHNOLOGIES(University of Missouri - Kansas City, 2024) Alsharef, Mrwah; Rulis, PaulMethylammonium lead bromide, known as CH3NH3PbBr3, is a promising perovskite material for the absorption layer in solar cells. While its bulk electronic structure is favorable, its long-term stability and interface design remain as primary concerns before it can be used for commercial production. Although experimental methods such as X-ray photoemission spectroscopy can be used to investigate the surface atomic and electronic structures of such materials (e.g., by observing core-level chemical shifts), theoretical support is vital for interpreting the measured data and for guiding the selection of future experiments. Unfortunately, perovskite solar cell materials often contain high Z-number atoms which require relativistic treatment. Here we show the development and implementation of scalar relativistic theory within the density functional theory (DFT) based Orthogonalized Linear Combination of Atomic Orbitals (OLCAO) method for electronic struc- ture calculation. We then demonstrate the application of the method to the calculation of core-level chemical shifts of all elements of CH3NH3PbBr3 and compared the results to those obtained with non-relativistic theory to evaluate the e↵ect of scalar relativistic theory. The results of the relativistic calculations were consistent with experimental expectations, enabling us to accurately calculate the chemical shift resulting from changes in the local en- vironment. In addition, the X-ray absorption near-edge structure (XANES) spectra of CH3NH3 and PbBr2 surface models were studied via depth pro- filing to highlight the influence of the surface e↵ects. The results indicate a shift towards lower energy of the edge onset for Pb-4f and Br-3d atoms in the CH3NH3 surface termination, while the edge onset of Pb-4f and Br-3d does not change for the PbBr2 surface termination. According to the findings, the modifications made on the surface of a material result in alterations in the edge onset.6 0Item Restricted DFT STUDY OF ELECTRONIC STRUCTURE AND MECHANICAL PROPERTIES OF CLAY MINERALS, AND USING LARGE-SCALE SUPERCELL MODELING FOR SOLVATED MONTMORILLONITE(University of Missouri–Kansas City, 2024-02-26) Shafei, Layla; Ching, Wai-YimClay mineral materials have attracted attention due to their many proper- ties and applications. The applications of clay minerals are closely linked to their structure and composition. Here, we studied the electronic structure properties of kaolinite, muscovite, and montmorillonite crystals, which are classified as clay minerals, by using DFT-based ab initio packages VASP and the OLCAO. This work aims to have a deep understanding of clay mineral materials, including electronic structure, bond strength, mechanical proper- ties, and optical properties. It is worth mentioning that understanding these properties may help continually result in new and innovative clay products in several applications, such as in pharmaceutical applications using kaolinite for their potential in cancer treatment, muscovite used as insulators in elec- trical appliances, and engineering applications that use montmorillonite as a sealant. In addition, our results show that the role played by hydrogen bonds in O-H bonds has an impact on the hydration in these crystals. Based on calculated total bond order density, it is concluded that kaolinite is slightly more cohesive than montmorillonite, which is consistent with the calculated mechanical properties. Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exother- mic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of struc- tural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio den- sity functional theory. The DFT calculation and analysis clarify important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk mod- ulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at -8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay.26 0Item Restricted Theory of quantum transport in nano scale structures(Lancaster University, 2024-01-29) Alharbi, Bader; Lambert, ColinIn the pursuit of future nano-scale applications within the field of molecular electronics, extensive investigations into electron transport through single molecules hold significant importance. As single or multiple molecules serve as crucial building blocks for designing and constructing molecular electronic devices, comprehending their electronic and transport properties becomes imperative. Countless theoretical and experimental studies have been conducted to create molecular junctions and explore their electrical performance. This thesis focuses on fundamental aspects of transport theory, employing theoretical and mathematical approaches to investigate electron transport through junctions, particularly involving a scattering region formed by a single molecule connected to metal electrodes. The research methods used are based on a combination of density functional theory, implemented within the SIESTA code, and non-equilibrium Green's function, realized using the GOLLUM code, to delve into electrical conductance on a molecular scale. The objective of this chapter is to address a puzzling paradox concerning meta connectivity, which exhibits destructive quantum interference (DQI) in a tight binding model. However, in certain instances, DQI does not manifest in a DFT calculation on the same system. To shed light on this inconsistency, a selection of molecules is examined, focusing on the distinction between meta and para connectivity. Two different types of linkers, thiol (-SH) and methyl sulphide (-SMe), are employed to couple different molecules to Au electrodes. Through this investigation, we aim to gain insights into the underlying factors that lead to the observed quantum interference behaviors. In project two, we conducted a comprehensive study, combining experimental and theoretical approaches, to explore charge transport in stacked graphene-like dimers. Our findings revealed that the interaction between room-temperature quantum interference and stacking significantly influences their highly non-classical electrical conductance. Notably, for the molecule CQI-L, the electrical conductance of the dimer exceeds that of the monomer by a remarkable factor of 25, attributed to the most energetically favorable stacking interactions. Conversely, for the molecule CQI-H, the dimer's conductance is approximately 40 times lower than that of the monomer. These results unequivocally demonstrate that precise control of connectivity to molecular cores, coupled with stacking interactions between their systems, provides a versatile avenue for modifying and optimizing charge transfer between molecules. This discovery is expected to inspire further vigorous research at both macroscopic and microscopic levels.19 0Item Restricted DENSITY FUNCTIONAL THEORY INVESTIGATIONS INTO METHANE ACTIVATION, OXIDATION, AND DIFFUSION ON IrO2(110), RuO2(110), AND MIXED METAL OXIDE MO2(110) (M=Ir & Ru)(Saudi Digital Library, 2023-12-01) Almarshad, Omar; Hibbitts, David; Weaver, JasonThe processes of methane adsorption and oxidation over late transition metal oxides of rutile type, as well as the adsorption and ensuing interaction of probabilistic species with the intermediate products of methane oxidation on the surfaces of iridium dioxide and ruthenium dioxide, and their various combinations, have been comprehensively examined utilizing the principles of density functional theory (DFT). Density functional theory calculations serve as a critical tool in this study, elucidating the stability of these mixed metal oxides, the energy dynamics of the corresponding reaction pathways, and the diffusion properties potentially influencing bifunctional reaction mechanisms. Further, DFT was employed to calculate reaction and activation-free energies pertinent to the methane reaction pathways on surfaces of IrO2(110) and mixed oxides. These computations provide valuable insights into the reaction mechanisms, critical structural properties, and the capacity of these pathways to function under steady-state catalytic conditions. This enhanced understanding permits the identification and mapping of the potential mechanisms that drive these reactions, contributing significantly to the body of knowledge on the structural properties that could determine the viability of these pathways under continuous catalytic conditions.40 0Item Restricted Metal Nitride Complexes as Potential Catalysts for C-H and N-H Bonds Activation(Saudi Digital Library, 2023-08-22) Alharbi, Waad; Cundari, ThomasTransition metal nitride complexes (TMNs) have shown excellent results in C-H activation applications in the last few decades. However, determining factors controlling the unique reactivity of the nitride ligand in TMNs is still poorly defined. Recognizing the dual ability of the nitride ligand to react as a nucleophile or an electrophile – depending on the metal and other supporting ligands – is a key to their broad-range reactivity; thus, three DFT studies were initiated to investigate these two factors effects (the metal and supporting ligands) for tuning nitride ligand reactivity for C-H and N-H bond activation/functionalization. We focused on studying these factors effects from both a kinetic and thermodynamic perspective in order to delineate new principles that explain the outcomes of TMN reactions. Chapter 2 reports a kinetic study of C–H amination of toluene to produce a new Csp3–N (benzylamine) or Csp2–N (para-toluidine) bond activated by diruthenium nitride intermediate. Studying three different mechanisms highlighted the excellent ability of diruthenium nitride to transform a C-H bond to a new C-N bond. These results also revealed that nitride basicity played an important role in determining C–H bond activating ability. Chapter 3 thus reports a thermodynamic study to map basicity trends of more than a one hundred TMN complexes of the 3d and 4d metals. TMN pKb(N) values were calculated in acetonitrile. Basicity trends decreased from left to right across the 3d and 4d rows and increases from 3d metals to their 4d congeners. Metal and supporting ligands effects were evaluated to determine their impacts on TMNs basicity. In Chapter 4 we sought correlations among basicity, nucleophilicity and enhanced reactivity for N–H bond activation. Three different mechanisms for ammonia decomposition reaction (ADR) were tested: 1,2-addition, nitridyl insertion and hydrogen atom transfer (HAT). Evaluating nitride reactivity for the aforementioned mechanisms revealed factors related to the metal and its attached ligands on TMNs for tuning nitride basicity and ammonia N–H activation barriers.14 0