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Molecular dynamics simulations of the oxidation of the Cu (100) surface using the COMB potential reveal a fairly low occurrence of reactions. Single point calculations of O2 on this surface predict that molecular dissociation only occurs when both O atoms are close to adjacent four fold hollow sites. The molecule dissociates to form a c(2x2) surface at low temperature and low oxygen coverage. At room temperature and with higher coverage, the surface reconstructs to a missing row (squared root of 2 \U+00d7\ 2 squared root of 2)R45° configuration. These findings are consistent with experimental observations.
This book presents a comprehensive review of the methods and approaches being adopted to push forward the boundaries of computational catalysis.
The depletion of fossil fuels necessitates alternate and clean energy sources. Lithium-ion batteries and solid oxide electrocatalysis devices are some of the most popular candidates. However, further improvements of these energy storage devices are essential in order to meet the ever-increasing global energy demand. Improvement of the performance of these high energy chemical systems is directly linked to the understanding and improving the complex physical and chemical phenomena and exchanges that take place at their different interfaces. Surfaces or interfaces, structures created between dissimilar media, such as liquids and solids, and interphases, structures arising in between these dissimilar media, present great challenges for their study and understanding since these are the regions where myriad events such as electron transfer, ion transfer and migration, reactions, and solvation/desolvation processes take place and significantly alter their landscape. In order to investigate the physical and chemical interactions at the interfaces of energy storage devices such as Li-ion batteries and solid oxide electrocatalysis devices, we used ReaxFF and eReaxFF reactive molecular dynamics simulations in the following research areas: 1) In the electrode/electrolyte interface of a typical lithium-ion battery a solid electrolyte interphase layer is formed as a result of electrolyte decomposition during the initial charge/discharge cycles. Electron leakage from anode to the electrolyte reduces the Li+-ion and makes them more reactive resulting in decomposition of the organic electrolyte. To study the Li-electrolyte solvation, solvent exchange and subsequent solvent decomposition reactions at the anode/electrolyte interface, we have extended existing ReaxFF reactive force field parameter sets to organic electrolyte species such as ethylene carbonate, ethyl methyl carbonate, vinylene carbonate and LiPF6 salt. Density Functional Theory (DFT) data describing Li-associated initiation reactions for the organic electrolytes and binding energies of Li-electrolyte solvation structures were generated and added to existing ReaxFF training data and subsequently, we trained the ReaxFF parameters with the aim to find the optimal reproduction of the DFT data. In order to discern the characteristics of Li neutral and cation, we have introduced a second Li parameter set to describe Li+-ion. ReaxFF is trained for Li-neutral and Li+-cation to have similar solvation energies but unlike the neutral Li, Li+ will not induce reactivity in the organic electrolyte. Solvent decomposition reactions are presumed to happen once Li+-ions are reduced to Li-atoms, which can be simulated using a Monte-Carlo type atom modification within ReaxFF. This newly developed force field is capable of distinguishing between a Li-atom and a Li+-ion properly. Moreover, it is found that the solvent decomposition reaction barrier is a function of the number of EC molecules solvating the Li-atom. 2) Graphene, a 2D material arranged in an sp2-bonded hexagonal network, is one of the most promising materials for lithium-ion battery anodes due to its superior electronic conductivity, high surface area for lithium intercalation, fast ionic diffusivity and enhanced specific capacity. A detailed atomistic modeling of electronic conduction and non-zero voltage simulations of graphitic materials require the inclusion of an explicit electronic degree of freedom. To enable large length and time scale simulations of electron conduction in graphitic anodes, we developed an eReaxFF force field describing graphitic materials with an explicit electron concept. The newly developed force field, verified against quantum chemistry-based data describing, amongst others, electron affinities and equation of states, reasonably reproduces the behavior of electron conductivity in pristine and imperfect graphitic materials at different applied temperatures and voltages. Our eReaxFF description is capable of simulating leakage of excess electrons from graphene which are captured by exposed lithium ions; a common behavior at the anode/electrolyte interface of a lithium-ion battery. Finally, the initiation of Li-metal-plating observed at the graphene surface reveals the eReaxFF force field's potential for the future development of Li-graphene interactions with explicit electrons. 3) Electrocatalysis results in the change of the rate of an electrochemical reaction occurring on an electrode surface by varying the electrical potential. Electrocatalysis can be used in hydrogen generation and the generated hydrogen can be stored for future use in fuel cells for clean electricity. The use of solid oxide in electrocatalysis specially in hydrogen evolution reaction is promising. To enable large length and time scale atomistic simulations of solid oxide electrocatalysis for hydrogen generation, we developed an eReaxFF force field for barium zirconate doped with 20 mol% of yttrium (BZY20). All parameters for the eReaxFF were optimized to reproduce quantum mechanical (QM) calculations on relevant condensed phase and cluster systems describing oxygen vacancies, vacancy migrations, water adsorption, water splitting and hydrogen generation on the surfaces of the BZY20 solid oxide. Using the developed force field, we performed zero-voltage molecular dynamics simulations to observe water adsorption and the eventual hydrogen production. Based on our simulation results, we conclude that this force field sets a stage for the introduction of explicit electron concept in order to simulate electron conductivity and non-zero voltage effects on hydrogen generation. Overall, the work described in this dissertation demonstrate how atomistic-scale simulations can enhance our understanding of processes at interfaces in energy storage materials.
This graduate-level textbook covers the major developments in surface sciences of recent decades, from experimental tricks and basic techniques to the latest experimental methods and theoretical understanding. It is unique in its attempt to treat the physics of surfaces, thin films and interfaces, surface chemistry, thermodynamics, statistical physics and the physics of the solid/electrolyte interface in an integral manner, rather than in separate compartments. It is designed as a handbook for the researcher as well as a study-text for graduate students. Written explanations are supported by 350 graphs and illustrations.
The amount of energy required to satisfy the demands of the human population may not be able to be supplied solely by fossil fuels as the world population continues to rise and the supply of fossil fuels starts to decline. Lithium-ion batteries (LIBs), since being suggested as commercialized energy storage systems by Sony company in the 1990s, have been considered an important device in alternative energy solutions owing to their high energy density, wide working voltage, long cycling life, and low self-discharge rate. Improvement of the performance of these high energy chemical systems is directly linked to the understanding and improving the complex physical and chemical phenomena and exchanges that take place at their different interfaces. Surfaces or interfaces, which means structures built between dissimilar media such as liquids and solids, and interphases, which means structures formed within these dissimilar media, present significant challenges for their study and understanding since these are the regions where myriad events such as electron transfer, ion transfer and migration, reactions, and solvation/desolvation processes occur and significantly alter their configuration. A detailed understanding of battery chemistry, especially the formation of a solid electrolyte interphase (SEI)--a thin passivation layer which is generated during the first charge cycle due to the reduction of electrolytes--is still elusive. It is well known that the SEI has a strong influence on the battery performance characteristics, such as irreversible capacity, safety, and cycle life, when the SEI is a thin layer between the liquid electrolytes and anode surfaces formed by the electrochemical reductive decomposition reaction of the electrolyte during the initial few cycles. A stable SEI with full surface coverage over the electrode is important for achieving optimal electrochemical performances of Li-ion batteries. Understanding the SEI is quite challenging due to its complicated and amorphous structure. In order to investigate the physical and chemical interactions at the interfaces of energy storage devices such as Li-ion batteries a, we used ReaxFF reactive molecular dynamics simulations in the following two research areas: 1. In the last decade silicon has attracted significant attention as a potential next generation anode material for Li-ion batteries (LIBs) due to its high theoretical specific capacity (3579 mAh/g (Li15Si4)) compared to that of the commonly used graphite (372 mAh/g). However, despite the apparent attractiveness of Si in view of its application in LIBs, it is known to suffer from severe degradation problems which lead to performance losses of Si-based anodes, and the electrochemical outcome of the degradation is well documented in the literature: rapid capacity fading of the anode accompanied by the increased internal resistance of the cell. Full utilization of silicon's potential as an anode material is thus prevented by incomplete understanding of the degradation mechanisms and the resulting inability to implement effective mitigation tactics. To study the Si anode degradation at the anode/electrolyte interface, we have developed a ReaxFF reactive force field simulation protocol. In this protocol, a delithiation algorithm is employed. This novel systematic delithiation algorithm helps to capture the effect of different delithiation rates, which plays an important role in the irreversible structural change of delithiated Si. Besides, the fundamental of degradation was investigated by analyzing the relationship between the depth of discharge and corresponding volume and structural changes at different rates. 2. The SEI (solid-electrolyte interphase) is important for protecting silicon anodes in batteries from losing both silicon and electrolyte through side reactions. A major issue with this technology is SEI breakdown caused by cracking in silicon particles. A strategy is presented for creating a self-sealing SEI that automatically covers and protects the cracked surface of silicon microparticle anodes by bonding an ion pair to the silicon surface. The cations in the bond prevent silicon-electrolyte reactions while the anions migrate to the cracked surface and decompose more easily than the electrolyte. The SEI formed in this way has a double layer structure with a high concentration of lithium fluoride in the inner layer. To study the electrode electrolyte reactions at the anode/electrolyte interface, we have developed ReaxFF reactive force field parameter sets to organic electrolyte species such as ethylene carbonate, N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), LiPF6 salt and lithium-Silicon oxygen electrode. Density Functional Theory (DFT) data describing Li-associated initiation reactions for the organic electrolytes and bonding energies of Li-electrolyte structures were generated and added to ReaxFF training data and subsequently, we trained the ReaxFF parameters with the aim to find the optimal reproduction of the DFT data. This force field is capable of distinguishing Li interaction with electrolyte in presence of self-sealing layer. Moreover, these findings provide a new way to design a stable SEI at the highly dynamic electrode-electrolyte interface. In addition to this battery work, we also studied halogen interaction with platinum surfaces, a system that has received considerable attention in catalysis and semiconductor mannufacturing. These halogen gases are applied as platinum mobilizers in both deposition and corrosion or etching processes since PtCl4 adsorption from an electrolyte and subsequent reduction to metallic Pt clusters is an electrochemical pathway for obtaining highly dispersed, catalytically active Pt surfaces. A novel ReaxFF reactive force field has been developed to understand the size and shape-dependent properties of platinum nanoparticles for the design of nanoparticle-based applications. The ReaxFF force field parameters are fitted against a quantum mechanical (QM) training set containing the adsorption energy of Cl and dissociative HCl on Pt (100) and Pt (111), the energy-volume relations of PtCl2 crystals, and Cl diffusion on Pt (100) and Pt (111). ReaxFF accurately reproduces the QM training set for structures and energetics of small clusters and PtClx crystals. The predictive capacity of the force field was manifested in molecular dynamics simulations of the Cl2 and HCl molecules interactions on the (100) and)111(surfaces of c-Pt crystalline solid slabs. The etching ratio between HCl and Cl2 are compared to experimental results, and satisfactory results are obtained, indicating that this ReaxFF protocol provides a useful tool for studying the atomistic-scale details of the etching process.
A complete reference to computer simulations of inorganic glass materials In Atomistic Simulations of Glasses: Fundamentals and Applications, a team of distinguished researchers and active practitioners delivers a comprehensive review of the fundamentals and practical applications of atomistic simulations of inorganic glasses. The book offers concise discussions of classical, first principles, Monte Carlo, and other simulation methods, together with structural analysis techniques and property calculation methods for the models of glass generated from these atomistic simulations, before moving on to practical examples of the application of atomistic simulations in the research of several glass systems. The authors describe simulations of silica, silicate, aluminosilicate, borosilicate, phosphate, halide and oxyhalide glasses with up-to-date information and explore the challenges faced by researchers when dealing with these systems. Both classical and ab initio methods are examined and comparison with experimental structural and property data provided. Simulations of glass surfaces and surface-water reactions are also covered. Atomistic Simulations of Glasses includes multiple case studies and addresses a variety of applications of simulation, from elucidating the structure and properties of glasses for optical, electronic, architecture applications to high technology fields such as flat panel displays, nuclear waste disposal, and biomedicine. The book also includes: A thorough introduction to the fundamentals of atomistic simulations, including classical, ab initio, Reverse Monte Carlo simulation and topological constraint theory methods Important ingredients for simulations such as interatomic potential development, structural analysis methods, and property calculations are covered Comprehensive explorations of the applications of atomistic simulations in glass research, including the history of atomistic simulations of glasses Practical discussions of rare earth and transition metal-containing glasses, as well as halide and oxyhalide glasses In-depth examinations of glass surfaces and silicate glass-water interactions Perfect for glass, ceramic, and materials scientists and engineers, as well as physical, inorganic, and computational chemists, Atomistic Simulations of Glasses: Fundamentals and Applications is also an ideal resource for condensed matter and solid-state physicists, mechanical and civil engineers, and those working with bioactive glasses. Graduate students, postdocs, senior undergraduate students, and others who intend to enter the field of simulations of glasses would also find the book highly valuable.
This book describes the forcefields/interatomic potentials that are used in the atomistic-scale and molecular dynamics simulations. It covers mechanisms, salient features, formulations, important aspects and case studies of various forcefields utilized for characterizing various materials (such as nuclear materials and nanomaterials) and applications. This book gives many help to students and researchers who are studying the forcefield potentials and introduces various applications of atomistic-scale simulations to professors who are researching molecular dynamics.
Machine learning methods are changing the way we design and discover new materials. This book provides an overview of approaches successfully used in addressing materials problems (alloys, ferroelectrics, dielectrics) with a focus on probabilistic methods, such as Gaussian processes, to accurately estimate density functions. The authors, who have extensive experience in this interdisciplinary field, discuss generalizations where more than one competing material property is involved or data with differing degrees of precision/costs or fidelity/expense needs to be considered.
The book is devoted to the consideration of the different processes taking place in thin films and at surfaces. Since the most important physico-chemical phenomena in such media are accompanied by the rearrangement of an intra- and intermolecular coordinates and consequently a surrounding molecular ensemble, the theory of radiationless multi-vibrational transitions is used for its description. The second part of the book considers the numerous surface phenomena. And in the third part is described the preparation methods and characteristics of different types of thin films. Both experimental and theoretical descriptions are represented. Media rearrangement coupled with the reagent transformation largely determines the absolute value and temperature dependence of the rate constants and other characteristics of the considered processes. These effects are described at the atomic or molecular level based on the multi-phonon theory, starting from the first pioneering studies through to contemporary studies.A number of questions are included at the end of many chapters to further reinforce the material presented. · Unified approach to the description of numerous physico-chemical phenomena in different materials· Based on the pioneering research work of the authors· Explantion of a variety of experimental observations· Material is presented at two levels of complexity for specialists and non-specialists · Identifies existing and potential applications of the processes and phenomena · Includes questions at the end of some chapters to further reinforce the material discussed
This book describes the rapidly expanding field of two-dimensional (2D) transition metal carbides and nitrides (MXenes). It covers fundamental knowledge on synthesis, structure, and properties of these new materials, and a description of their processing, scale-up and emerging applications. The ways in which the quickly expanding family of MXenes can outperform other novel nanomaterials in a variety of applications, spanning from energy storage and conversion to electronics; from water science to transportation; and in defense and medical applications, are discussed in detail.