Condensed Matter Physics Commons^™

First Principles Calculation Of Electron-Phonon Coupling In Nonequilibrium Quantum Materials, Chendi Xie

All Dissertations

This dissertation combines first-principles computation and light-induced nonequilibrium analysis to understand and control electron–phonon coupling (EPC) and emergent many-body phenomena in quantum materials, in both equilibrium and nonequilibrium states.

Chapters 1 and 2 build the theoretical and computational foundation, beginning with electron and phonon self-energies, linewidths, and perturbation theory for EPC, followed by density functional theory (DFT) and density functional perturbation theory (DFPT), which serve as the first-principles workhorses used throughout. Chapter 3 reviews Bardeen-Cooper-Schrieffer (BCS) and Migdal-Eliashberg theory, including the BCS gap - transition temperature (T_c) relation and the strong-coupling generalization, and delineates the practical validity bound …

Ab Initio Studies On Mechanical Properties Of Freestanding Ferroic Monolayers, John Malcolm Davis

Graduate Theses and Dissertations

This thesis explores the role of mechanical properties and elastic couplings in freestanding paradigmatic ferroic monolayers within the framework of density functional theory. This dissertation is comprised of three interconnected published studies: (i) establishing the elastic behavior across a temperature-driven phase transition in SnSe monolayers; (ii) thermally-driven phase transitions in graphene-like silicene, germanene, and stanene, examining the structural stability and band gap occlusion; and (iii) magnetoelastic coupling in an Ising-like CrSiTe3 monolayer, focused on assessing magnetic contributions to the material stiffness by establishing a proper non-magnetic reference.

Investigating The Roles Of Intrinsic Point Defects And Transition Metal Doping In Monolayer And Bulk Tis2, Patrick J. Keeney

UNF Graduate Theses and Dissertations

Within this thesis, the magnetic and electronic properties of various 1T-TiS₂ systems are thoroughly examined using density functional theory (DFT) and scanning tunneling microscopy (STM). Formation energies and electronic implications of intrinsic point defects in bulk TiS₂ and monolayer TiS₂ are analyzed by approximating a computational monolayer of TiS₂ as the surface layer of a bulk sample. This approximation is validated given that intralayer covalent bonding dominates interlayer van der Waals interactions. We conclude that the most energetically favorable intrinsic defects are Ti atoms settling above the outermost S plane and S vacancies. In addition, the …

Dynamic Exchange-Correlation Functional For Bandgap Optimization: Reparametrization And Machine Learning, Viviana Faride Dovale Farelo

Graduate Theses, Dissertations, and Problem Reports (ETD)

This dissertation explores predicting the physical properties of solids using first-principles methods, with a focus on Density Functional Theory (DFT). DFT uses the electronic density within a material to predict its properties, simplifying the treatment of electron-electron interactions and allowing the study of realistic systems with a balanced treatment between accuracy and computational efficiency. Additionally, machine learning (ML) is employed to create correlations between some physical properties of solids and other properties or parameters that are more difficult to calculate.

The main problem addressed in this study is adjusting the parameters in the Strongly Constrained and Appropriately Normed (SCAN) semilocal …

Quantum Capacitance Investigation Of Different Tas2 Polymorphs For Energy Storage Applications – First Principles Study, Mahmoud Elattar

Theses and Dissertations

Energy is an essential requirement, which has a growing demand due to the growth of population and the world transformation into electronic. More than 70% of energy resources are fossil-fuel based which has an environmental impact due to the CO₂ emissions. Energy hubs for Fossil-fuel to electric energy conversion, controlled CO₂ emissions processing units, and energy storage system are key factors for a smooth transition to green energy without lack of energy supplies, where electrical energy storage systems (ESS) are key enablers to achieve that. One of the effective components which determines the ESS efficiency is the electrode …

First Principle Studies Of The Effects Of Alkali-Metal Intercalation On Structural Transition From Black To Blue Phosphorene And The Adsorption Of N2h4 On Ws2 Layers., Md Rajib Khan Musa

Electronic Theses and Dissertations

A comprehensive density functional theory calculation has been conducted to seek a potential structural transition from black to blue phosphorene layers, with a focus on the roles played by alkali-metal intercalation in black phosphorene/phosphorus. This study reveals that at sufficiently high Li concentration and specific, well-defined configurations, a phase transition from black to blue phosphorene can take place. The Li atoms intercalated in black phosphorene could act as a “catalyst” in the“reactive region” of the lone pair of P atoms, leading to a P-P bond breaking and, subsequently, a local structural transformation from an orthorhombic lattice to an assembly of …

Transport Properties Of Binary And Doped Diborides, Alin Babu Niraula

Graduate Theses/Dissertations

A systematic computational study to evaluate the electronic structures and transport properties including resistivity, thermal conductivity of several binary diborides (ZrB2 , TiB2 , TaB2 , CrB2 , and AlB2 ) and the ZrB2 alloyed with Cr, Al, Ti and Ta has been performed. Due to the p-d hybridization, the characteristic pseudo gap at the Fermi energy level (Ef) from the density of states (DOS) is presence in the DOS of both ZrB2 and TiB2 in contrast to those of TaB2 and CrB2 with only a partial occupation on the anti-bonding states. AlB2 is also similarly shown the presence of …

First-Principles Studies Of Anion Engineering In Functional Ceramics, Steven Timothy Hartman

McKelvey School of Engineering Graduate Student Theses & Dissertations

Ceramic materials display a wide variety of valuable properties, such as ferroelectricity, superconductivity, and magnetic ordering, due to the partially covalent bonds which connect the cations and anions. While many breakthroughs have been made by mixing multiple cations on a sublattice, the equivalent mixed-anion ceramics have not received nearly as much attention, despite the key role the anion plays in the materials’ properties. There is great potential for functional ceramics design using anion engineering, which aims to tune the materials properties by adding and removing different types of anions in existing classes of ceramic materials. In this dissertation, I present …

Magnetism In Γ-Fesi2 Nanostructures: A First Principles Study, Sahil Dhoka

Dissertations, Master's Theses and Master's Reports

First-principles calculations are performed on γ-FeSi₂ nanostructures grown on Si (111) and (001) substrate. An attempt to explain the origin of emergent magnetic properties of the metastable gamma phase of iron di-silicide (γ-FeSi₂) is made, which show ferromagnetic behavior on nanoscale, unlike its possible bulk form. Many papers try to explain this magnetism from factors like bulk, epitaxial strain, interface, surface, edges, and corners but doesn’t provide an analytical study for these explanations. Density functional theory is used to analyze the magnetic effects of these factors. The results for the epitaxial structures show no magnetic behavior for …

Electronic And Geometric Structure Of Alnom And Alnom +, Albert R. Armstrong

Theses and Dissertations

Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of Al_nO_m (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al_2nO_3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al₄O₄, Al₅O₃, Al …

Computational Prediction, Characterization, And Methodology Development For Two-Dimensional Nanostructures: Phosphorene And Phosphide Binary Compounds., Congyan Zhang

Electronic Theses and Dissertations

In this thesis, a comprehensive computational simulation was carried out for predicting, characterizing, and applications of two-dimensional (2D) materials. The newly discovered GaP and InP layers were selected as an example to demonstrate how to explore new 2D materials using computational simulations. The performance of phosphorene as the anode material of Lithium-ion battery was discussed as the example of the application of 2D material. Furthermore, the semi-empirical Hamiltonian for phosphorous and lithium elements have been developed for our future work on the application of phosphorus and lithium-based systems. The novel 2D materials of GaP and InP binary compounds were found …