Download or read book Understanding Structure Thermodynamics and Dynamics of Silica Liquids and Glasses Using Atomistic Simulations and Machine Learning written by Zheng Yu and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Glass materials are found all around us, but fundamental questions about the nature of their amorphous structures and formation processes remain unsolved after decades of research. In this dissertation, silica, an archetype glass former, is taken as an example glass for investigations into glass structures, thermodynamics, dynamics, two-level systems (TLS), and atomic interactions based on molecular dynamics simulations and machine learning methods. Specifically, we investigate the structure-thermodynamic stability relationship using a library of silica inherent structures generated from melt-quench and replica exchange molecular dynamics simulations. Based on machine learning, we find that short-range and medium-range features play very different roles on the glass stability across the liquid and glass regions. We then revisit an interesting dynamical transition in silica liquid, the fragile-to-strong transition (FTS), from the perspective of microscopic dynamics. By machine learning to classify atomic rearrangements, the FTS is found to originate from the two types of energy barriers in silica, representing a fast and a slow microscopic dynamics channel. The fast channel controlled by the short-range defects closes rapidly with decreasing temperature, causing the fragility crossover. A similar approach is also applied to investigate TLS. We predict TLS densities in a large number of inherent structures with a variety of glass stability using machine learning and verify them using molecular dynamics simulations. We find a decrease in the TLS density with the fictive temperature, which can be described by a quadratic function as suggested by the random first-order transition theory. Lastly, we introduce a linear machine learning force matching approach that can directly extract pair atomic interactions from ab initio calculations in amorphous materials. This approach is applied to silica to understand the atomic interactions within its structure and develop a new classical force field. Through the comprehensive fundamental investigations on the nature of silica glass and liquid, I hope the understandings and methods presented in this dissertation can be transferred to study other glass-forming systems.

Download or read book Atomistic Simulations of Glasses written by Jincheng Du and published by John Wiley & Sons. This book was released on 2022-04-05 with total page 564 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Atomistic Contribution to the Understanding of Metallic and Silica Glasses written by Pawel Koziatek and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Amorphous materials are ubiquitous in everyday life. They comprise "hard" and"soft" glasses. Hard amorphous systems are usually seen as structure materials, with properties and use comparable to those of crystalline solids. Soft glasses are usually seen as complex fluids, described in terms of their rheological properties with the corresponding practical applications (concrete, paints, drilling mud, cosmetic gels, creams or foams, etc). Amorphous materials can either present a solid-like behaviour or flow depending on their mechanical load: all are yield-stress fluids. Their usage limits are often defined by the occurrence of shear-banding, an extreme form of localization seen in molecular glasses as well as in granular materials. There is now considerable evidence that they are consequences of the existence of a disordered structure at the level of the elementary constituents (atoms, particles,...). Studies of plasticity in amorphous solids, are still hampered by the lack of any identifiable defect responsible for the plastic response. It is now acknowledged that plasticity is the net result of local rearrangements, or "shear transformations", involving small clusters of (say a few tens of) particles. These rearrangements are thermally--activated and are ubiquitous processes in the structural relaxation and deformation of glasses at low temperatures. Unfortunately, they take place over timescales long compared to those accessible to direct Molecular Dynamics simulations. Some extremely promising new tools, however, are opening the route towards accelerated algorithms for the simulation of thermal systems. They are based on numerical methods developed over these last two decades to determine thermally activated transitions in atomic systems. Of particular interest here is the Activation-Relaxation Technique (ART), an eigenvector-following method that allows the identification of activated states and paths in the potential energy landscape of atomic systems. In this study, we will show that although an exhaustive search for saddle points in case of disordered solids is unfeasible (because of the exponential number of activated states), ART can identify enough saddles to build statistically relevant samples, from which stationary distributions can be computed. The purpose of this strictly numerical thesis was the prediction of thermally activated kinetics in glasses such as those encountered experimentally. The nature of such miscroscopic events occuring in disordered systems was studied both under mechanical stress and in ageing conditions. We investigate two quantities that describe thermally-activated events within the harmonic approximation of the transition state theory, i.e. activation energy and attempt frequency.Since in the definition of an attempt frequency the curvature of the initial minimum and the saddle point are present, we wanted to see if there was a relation between attempt frequencies and activation energies of a given event in two types of systems: metallic glasses and silica glasses. Such correlation had been observed before for a wide range of phenomena and is referred to as the Meyer-Neldel compensation rule. We also attempt to answer if the simple BKS potential without Ewald summation is able to reproduce polyamorphism observed in silica glasses subject to hydrostatic compression and characterized mainly in terms of coordination numbers. Apart from thermally activated processes, the structural analyses of metallic and silica glasses were performed. The short and medium range orders were characterized using two methods: Voronoi tesselations for metallic glasses, providing us information about near neighbor conformations, and in case of silica, statistics of ring distributions.

Download or read book Computer Simulation of Silica written by Ivan Saika-Voivod and published by . This book was released on 2002 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structural Glasses and Supercooled Liquids written by Peter G. Wolynes and published by John Wiley & Sons. This book was released on 2012-04-10 with total page 422 pages. Available in PDF, EPUB and Kindle. Book excerpt: With contributions from 24 global experts in diverse fields, and edited by world-recognized leaders in physical chemistry, chemical physics and biophysics, Structural Glasses and Supercooled Liquids: Theory, Experiment, and Applications presents a modern, complete survey of glassy phenomena in many systems based on firmly established characteristics of the underlying molecular motions as deduced by first principle theoretical calculations, or with direct/single-molecule experimental techniques. A well-rounded view of a variety of disordered systems where cooperative phenomena, which are epitomized by supercooled liquids, take place is provided. These systems include structural glasses and supercooled liquids, polymers, complex liquids, protein conformational dynamics, and strongly interacting electron systems with quenched/self-generated disorder. Detailed calculations and reasoned arguments closely corresponding with experimental data are included, making the book accessible to an educated non-expert reader.

Download or read book Atomistic simulations of Silicate Glasses written by Seung Ho Hahn and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicate-based glasses are one of the most versatile materials in terms of technological perspective with a wide range of industrial applications. In most cases, glass products are exposed to various aqueous environments (either humid air or liquid water) and subject to physical contact with foreign objects, which leads to deterioration of chemical and mechanical properties of glass surfaces. Therefore, understanding their interactions with adsorbed interfacial water molecules is critical as it can provide physical insights needed for rational design of more durable glasses. Experimental characterization approaches have been applied to tackle difficult problems associated with the complex nature of glass surfaces but they are often limited by the time-scale resolution. As a result, they have failed to offer important structural characteristics and chemical reaction mechanisms under dynamic processes happening at the glass surface. To complement the challenges that experimental endeavors are encountering, this dissertation aims to provide a comprehensive understanding of water interactions of silicate glass surfaces using atomistic-scale simulations techniques. In particular, ReaxFF reactive force field-based molecular dynamics (MD) simulations are employed to study two distinct surface phenomena, i) surface water reaction and ii) surface mechanochemical wear process. These studies represent the surface damage process of silicate glass in the absence and presence of mechanical actions, respectively. The first part of this dissertation describes the water interactions of a silicate glass with readily leachable alkali (sodium) ions. In this study, highly complex surface chemistry, including proton/water exchange with the sodium ions, formation of relatively long-living sodium-hydroxide ionic complexes at the glass surface and eventual dissolution of those ion pairs into the water phase are described. Also, surface mapping of water binding energy to the glass surface is evaluated at different stages of the glass-water reaction, which would be relevant to assess the chemical durability of the glass materials based on the glass network topology. After the transport behavior and glass-water reaction mechanism at the surface has been identified, the mechanochemical wear process of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules is covered in the second part of this dissertation. The effect of water molecules on the shear-induced chemical reaction at the sliding interface was investigated and the dependence of wear on the number of interfacial water molecules in ReaxFF-MD simulations was found to be qualitatively in reasonable agreement with the experimental data. The large-scale atomistic simulation approaches with ReaxFF reactive force field presented in this dissertation alleviates the limitations of DFT calculations and experiments, providing new and meaningful insights on the chemical dynamics associated within the glass-water interface.

Download or read book Predicting the Young s Modulus of Silicate Glasses by Molecular Dynamics Simulations and Machine Learning written by Kai Yang and published by . This book was released on 2020 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the compositional dependence of properties of silicate glass is critical to design novel glasses for various technology applications. With the development in molecular dynamics simulations and machine learning techniques, a combined and fully computational approach, which is able to reveal the relationship between glass composition and its mechanical properties, can be developed and served as a guide prior to experiments and manufacturing. On one hand, machine learning is a powerful tool to predict the properties based on the existing database. On the other hand, molecular dynamics simulation cannot only produce sufficient data points for machine learning models but also provide a detailed picture of the atomic structure of glasses. This atomic-scale knowledge from molecular dynamics simulation contains an intrinsic relationship between glass compositions and their mechanical properties. Here, we first use molecular dynamics simulation to generate the dataset for calcium aluminosilicate glasses and apply different machine learning models to predict their Young's modulus using glass compositions in Chapter 1. Next, we apply topological constraint theory to quantify the atomic structures of simulated glasses and use this knowledge to predict Young's modulus for calcium aluminosilicate glass family in Chapter 2. Last, in Chapter 3, we propose a fully analytical model to link the network topology with glass compositions.

Download or read book Molecular Dynamics of Glass Forming Systems written by George Floudas and published by Springer Science & Business Media. This book was released on 2010-11-25 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pressure is one of the essential thermodynamic variables that, due to some former experimental difficulties, was long known as the “forgotten variable.” But this has changed over the last decade. This book includes the most essential first experiments from the 1960's and reviews the progress made in understanding glass formation with the application of pressure in the last ten years. The systems include amorphous polymers and glass-forming liquids, polypeptides and polymer blends. The thermodynamics of these systems, the relation of the structural relaxation to the chemical specificity, and their present and future potential applications are discussed in detail. The book provides (a) an overview of systems exhibiting glassy behavior in relation to their molecular structure and provides readers with the current state of knowledge on the liquid-to-glass transformation, (b) emphasizes the relation between thermodynamic state and dynamic response and (c) shows that the information on the pressure effects on dynamics can be employed in the design of materials for particular applications. It is meant to serve as an advanced introductory book for scientists and graduate students working or planning to work with dynamics. Several scientific papers dealing with the effects of pressure on dynamics have appeared in leading journals in the fields of physics in the last ten years. The book provides researchers and students new to the field with an overview of the knowledge that has been gained in a coherent and comprehensive way.

Download or read book The Vitreous State written by Ivan S. Gutzow and published by Springer Science & Business Media. This book was released on 2013-04-12 with total page 566 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book summarizes the experimental evidence and modern classical and theoretical approaches in understanding the vitreous state, from structural problems, over equilibrium and non-equilibrium thermodynamics, to statistical physics. Glasses, and especially silicate glasses, are only the best known representatives of this particular physical state of matter. Other typical representatives include organic polymer glasses, and many other easily vitrifying organic and inorganic substances, technically important materials, amidst them vitreous water and vitrified aqueous solutions, and also many metallic alloy systems. Some of these systems only form glasses under particular conditions, e.g. through ultra-rapid cooling. This book describes the properties and the formation of both every-day technical glasses and especially of such more exotic forms of vitreous matter. It is a unique source of knowledge and new ideas for materials scientists, engineers and researchers working on condensed matter. The new edition emphasizes latest experimental findings and modern theories, explaining the kinetics of glass formation, the relaxation and stabilization of glasses and their crystallization in terms of new models, derived from the framework of the thermodynamics of irreversible processes. It shows how the properties of common technical glasses, window glass, or the vitreous ice kernel of comets can be used to develop a new understanding of the existence of matter in various, unusual forms. The described theories can even find application for the description of lasers and interesting unusual processes in the universe.

Download or read book Reactions and Interfacial Behaviors of the Water Amorphous Silica System from Classical and Ab Initio Molecular Dynamics Simulations written by Jessica M. Rimsza and published by . This book was released on 2016 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to the wide application of silica based systems ranging from microelectronics to nuclear waste disposal, detailed knowledge of water-silica interactions plays an important role in understanding fundamental processes, such as glass corrosion and the long term reliability of devices. In this dissertation, atomistic computer simulation methods have been used to explore and identify the mechanisms of water-silica reactions and the detailed processes that control the properties of the water-silica interfaces due to their ability to provide atomic level details of the structure and reaction pathways. The main challenges of the amorphous nature of the silica based systems and nano-porosity of the structures were overcome by a combination of simulation methodologies based on classical molecular dynamics (MD) simulations with Reactive Force Field (ReaxFF) and density functional theory (DFT) based ab initio MD simulations. Through the development of nanoporous amorphous silica structure models, the interactions between water and the complex unhydroxylated internal surfaces identified the unusual stability of strained siloxane bonds in high energy ring structure defects, as well as the hydroxylation reaction kinetics, which suggests the difficulty in using DFT methods to simulate Si-O bond breakage with reasonable efficiency. Another important problem addressed is the development of silica gel structures and their interfaces, which is considered to control the long term residual dissolution rate in borosilicate glasses. Through application of the ReaxFF classical MD potential, silica gel structures which mimic the development of interfacial layers during silica dissolution were created A structural model, consisting of dense silica, silica gel, and bulk water, and the related interfaces was generated, to represent the dissolution gel structure. High temperature evolution of the silica-gel-water (SGW) structure was performed through classical MD simulation of the system, and growth of the gel into the water region occurred, as well as the formation of intermediate range structural features of dense silica. Additionally, hydroxylated silica monomers (SiO4H4) and longer polymerized silica chains were formed in the water region, indicating that glass dissolution is occurring, even at short time frames. The creation of the SGW model provides a framework for a method of identifying how interfacial structures which develop at glass-water interfaces can be incorporated into atomistic models for additional analysis of the dissolution of silicates in water.

Download or read book Structure Thermophysical Properties of Liquids and Their Connection with Glass Formability written by Rongrong Dai and published by . This book was released on 2020 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metallic glasses have drawn significant attention due to their unique properties, such as high strength, excellent elastic energy storage capacity, and versatile processability. However, why some liquids can easily form metallic glasses while others don't is still unclear. Since metallic glasses are formed when liquids are cooled fast enough to bypass crystallization, we hope to better understand glass formation by investigating the structural evolution and thermophysical properties of the liquids as they are cooled toward the glass transition. Multiple molecular dynamics simulations suggest a crossover temperature for the dynamics near the liquidus temperature, which corresponds to the onset of cooperative structural rearrangements and may be the beginning of the glass transition. In this dissertation, a possible structural signature of this onset of cooperativity is first identified using high-energy synchrotron X-ray scattering studies and viscosity measurements on electrostatically levitated liquids. We also address the practical question of how to predict glass formation from properties of the high temperature liquids. A method to accurately predict the glass transition temperature in metallic glasses from properties of the equilibrium liquids is proposed. It uses the viscosity and the thermal expansion coefficient for the equilibrium liquid. Using the predicted glass transition temperature and a fragility parameter developed from the liquid properties, a new prediction formula is generated, which only uses the liquid properties. While the prediction formula works for most cases, in some cases, it fails. The analysis of these anomalous cases demonstrates that the structural similarity between the liquid and crystal phases plays an important role in the glass formability. This is the first demonstration of this important controlling factor for glass formability. We also used machine learning (Lasso regression and Random Forest) to predict the glass formability and identify important predictors. The identified important predictors are in good agreement with those from the empirical rules. Finally, the evolution of the Cu46Zr54 liquid structure is investigated by elastic neutron scattering (with isotopic substitution) and synchrotron X-ray scattering studies. The experimental results show that the number of Cu-Cu and Zr-Zr atom pairs increases as the temperature decreases, while the number of Cu-Zr atom pairs decreases on cooling. This result disagrees with predictions from previous molecular dynamics studies, suggesting that the potentials used in the molecular dynamics simulations should be reassessed.

Download or read book Structural Chemistry of Glasses written by K.J. Rao and published by Elsevier. This book was released on 2002-06-26 with total page 585 pages. Available in PDF, EPUB and Kindle. Book excerpt: Structural Chemistry of Glasses provides detailed coverage of the subject for students and professionals involved in the physical chemistry aspects of glass research. Starting with the historical background and importance of glasses, it follows on with methods of preparation, structural and bonding theories, and criteria for glass formation including new approaches such as the constraint model. Glass transition is considered, as well as the wide range of theoretical approaches that are used to understand this phenomenon. The author provides a detailed discussion of Boson peaks, FSDP, Polymorphism, fragility, structural techniques, and theoretical modelling methods such as Monte Carlo and Molecular Dynamics simulation. The book covers ion and electron transport in glasses, mixed-alkali effect, fast ion conduction, power law and scaling behaviour, electron localization, charged defects, photo-structural effects, elastic properties, pressure-induced transitions, switching behaviour, colour, and optical properties of glasses. Special features of a variety of oxide, chalcogenide, halide, oxy-nitride and metallic gasses are discussed. With over 140 sections, this book captures most of the important and topical aspects of glass science, and will be useful for both newcomers to the subject and the experienced practitioner.

Download or read book Dynamical Heterogeneities in Glasses Colloids and Granular Media written by Ludovic Berthier and published by OUP Oxford. This book was released on 2011-07-14 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most of the solid materials we use in everyday life, from plastics to cosmetic gels exist under a non-crystalline, amorphous form: they are glasses. Yet, we are still seeking a fundamental explanation as to what glasses really are and to why they form. In this book, we survey the most recent theoretical and experimental research dealing with glassy physics, from molecular to colloidal glasses and granular media. Leading experts in this field present broad and original perspectives on one of the deepest mysteries of condensed matter physics, with an emphasis on the key role played by heterogeneities in the dynamics of glassiness.

Download or read book Atomistic Simulation of Fluid Structure and Diffusion in Functionalized Mesoporous Silica written by Hamzeh Kraus and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Statistical Physics of Crystals and Liquids written by Duane C. Wallace and published by World Scientific. This book was released on 2002 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presents a unified formulation from first principles of the Hailtonian and statistical mechanics of metallic and insulating crystals, amorphous solids, and liquids.

Download or read book Atomistic Modelling and Prediction of Glass Forming Ability in Bulk Metallic Glasses written by Sina Sedighi and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Molecular Dynamics Simulations of Metallic Glass Formation and Structure written by David C. Riegner and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Metallic glasses, a class of metal alloys which lack a periodic crystal structure, exhibit exceptional property combinations not accessible by other classes of materials. In spite of promise for widespread application, metallic glasses are difficult to synthesize and understanding of their structure and behavior is limited compared to crystalline alloys. There is no predictive criterion for determining if a particular alloy is capable of forming glass. Numerous glass-forming alloys have been reported, spanning a wide range of possible properties largely through trial and error. Engineering of these materials is difficult, as the connection between atomic structure and macroscopic behavior is not sufficiently developed to exploit particular behaviors in any intentional capacity. Using Molecular Dynamics (MD) simulations, three metallic glass-forming systems, Al-La, Cu-Zr and Cu-Ti-Zr were investigated and compared with the intention of connecting structure to properties and illuminating differences in glass-forming behavior in different alloys. From these simulations a specific mechanism occurring in the liquid, the changing of nearest neighbor environments, was identified and correlated to liquid viscosity. The change in viscosity with temperature, called fragility, was connected to this atomic-scale behavior allowing glass formers and non-glass formers in the Al-La alloys system to be separated from each other. The structure of each glass is readily available from these simulations, and the changes to neighbor environments in Al-La and Cu-Zr alloys, were found to be very similar when comparing the smaller atom type (Al, Cu). Differences in system-wide behavior for Al-La and Cu-Zr can be described based upon the behavior of the larger atom type (La, Zr), where Zr causes a major change in behavior as the majority component not exhibited by even very La-rich alloys. This dissimilarity between La and Zr provides a plausible explanation for Cu-Zr’s superior glass-forming ability compared to Al-La. Experimental data indicated that Cu-Ti-Zr achieve maximum glass-forming ability near Cu51.7Zr36.7Ti11.6. The addition of Ti to the Cu-Zr binary system causes a decrease in nearest-neighbor-switching events and stabilizes structures formed in the liquid, rather than destroying them. Cu51.7Zr36.7Ti11.6 also divides two compositional regions of hardness dependence: above 37% Zr the hardness scales with the concentration of Cu, while below 37% Zr the hardness scales with the concentration of Ti. Based on concepts developed for Al-La and Cu-Zr it was revealed that removing Cu drastically reduced the number of efficiently-packed Cu-centered structures. Below 37% Zr this effect is compensated by an increase in other dense structures but above 37% the effect is both more potent and uncompensated. The loss of these structures is responsible for the changes in yield behavior, and has an effect on the GFA. Finally, extension of these simulations to additional systems requires new multi-component EAM potentials, an essential input for MD simulations. The Rapid Alloy Method for the Production of Accurate General Empirical Potentials (RAMPAGE) was developed to create new multi-component potentials from elemental potentials available in the literature. Using RAMPAGE, the characteristics identified in glass-forming systems can be investigated in other metallic systems.