Predicting crystal growth via a unified kinetic three-dimensional partition model

Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years1, 2, 3, 4, 5, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy6, 7, 8. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system9, 10, 11. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into ‘natural tiles’ or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal–organic frameworks, calcite, urea and L-cystine

KIMERA: A Kinetic Montecarlo Code for Mineral Dissolution

KIMERA is a scientific tool for the study of mineral dissolution. It implements a reversible Kinetic Monte Carlo (KMC) method to study the time evolution of a dissolving system, obtaining the dissolution rate and information about the atomic scale dissolution mechanisms. KIMERA allows to define the dissolution process in multiple ways, using a wide diversity of event types to mimic the dissolution reactions, and define the mineral structure in great detail, including topographic defects, dislocations, and point defects. Therefore, KIMERA ensures to perform numerous studies with great versatility. In addition, it offers a good performance thanks to its parallelization and efficient algorithms within the KMC method. In this manuscript, we present the code features and show some examples of its capabilities. KIMERA is controllable via user commands, it is written in object-oriented C++, and it is distributed as open-source software.Spanish Ministry of Economy, Industry and Competitiveness (project Ref-201860I057) and the Spanish Ministry of Science, Innovation and Universities (project Ref RTI2018-098554-B-I00). P. Martin acknowledges support from the PhD scholarship Tecnalia Research & Innovation’s grant

A Computational Study of Material Transformations in Glass Forming Systems

Amorphous solids (glasses) are a class of materials that lack the traditional long-range order found in crystals, and are primarily formed by rapid cooling of a liquid to bypass crystal nucleation. Their lack of crystallinity and associated defects gives them useful electromagnetic and mechanical properties. However, the affinity of a material to vitrification is only loosely understood, and structural detail is difficult to obtain via traditional methods. This thesis firstly investigates the promotion of glass formation via crystal inhibition. Molecular dynamics simulations of binary alloys are used to show crystal frustration via specific interactions of interaction range and particle softness, resulting in a lower enthalpic drive and complex crystal structures. Secondly, a facilitated kinetic Ising model is used to investigate the dynamics of organic glasses in solution. Glass dissolution is shown to have a non-linear dependence on the effective temperature of the solute, switching between a front-like dissolution at low temperatures, and a diffuse interface at higher temperatures. Also shown is a method of preparing an enhanced glass via precipitation from a solution, capable of creating a much lower energy glass than simple bulk cooling

Study of mineral dissolution by kinetic Monte Carlo simulations.

172 p.El método Monte Carlo Cinético es el complemento perfecto de las simulaciones atómicas debido a su poder para llevar sus resultados a escalas espaciales y temporales comparables con los experimentos. Juntos contribuyen a predecir y entender las propiedades de sistemas reales y extender el conocimiento más allá de los límites experimentales. En esta tesis hemos aplicado el Monte Carlo Cinético junto con un novedoso modelo para estudiar la disolución de los minerales, lo que nos ha permitido responder a algunas preguntas sin resolver detrás de los mecanismos de disolución a escala atómica. Además, la concordancia de nuestro modelo con los resultados experimentales nos ha animado a desarrollar KIMERA, un programa en C++ capaz de estudiar la disolución de una multitud de minerales con resolución atómica.Tecnali

Study of mineral dissolution by kinetic Monte Carlo simulations.

172 p.El método Monte Carlo Cinético es el complemento perfecto de las simulaciones atómicas debido a su poder para llevar sus resultados a escalas espaciales y temporales comparables con los experimentos. Juntos contribuyen a predecir y entender las propiedades de sistemas reales y extender el conocimiento más allá de los límites experimentales. En esta tesis hemos aplicado el Monte Carlo Cinético junto con un novedoso modelo para estudiar la disolución de los minerales, lo que nos ha permitido responder a algunas preguntas sin resolver detrás de los mecanismos de disolución a escala atómica. Además, la concordancia de nuestro modelo con los resultados experimentales nos ha animado a desarrollar KIMERA, un programa en C++ capaz de estudiar la disolución de una multitud de minerales con resolución atómica.Tecnali

<i>CrystalGrower</i>: a generic computer program for Monte Carlo modelling of crystal growth.

From Europe PMC via Jisc Publications RouterHistory: ppub 2020-11-01, epub 2020-11-18Publication status: PublishedA Monte Carlo crystal growth simulation tool, CrystalGrower, is described which is able to simultaneously model both the crystal habit and nanoscopic surface topography of any crystal structure under conditions of variable supersaturation or at equilibrium. This tool has been developed in order to permit the rapid simulation of crystal surface maps generated by scanning probe microscopies in combination with overall crystal habit. As the simulation is based upon a coarse graining at the nanoscopic level features such as crystal rounding at low supersaturation or undersaturation conditions are also faithfully reproduced. CrystalGrower permits the incorporation of screw dislocations with arbitrary Burgers vectors and also the investigation of internal point defects in crystals. The effect of growth modifiers can be addressed by selective poisoning of specific growth sites. The tool is designed for those interested in understanding and controlling the outcome of crystal growth through a deeper comprehension of the key controlling experimental parameters

Molecular Dynamics Simulation of the Structure, Dynamics and Crystallization of Ionic Liquids under Confinement and Low Temperature

Ionic liquids (ILs) have sparked widespread interest due to their peculiar properties and the resulting possibility of manifold applications. In this dissertation, molecular dynamics (MD) simulations have been used to elucidate the dynamics, structure and crystallization of ionic liquids in the bulk and confinement. First we studied the properties of the ILs [dmim+][Cl-] and [emim+][NTf2-] when they are confined inside nanomaterials such as CMK-3, CMK-5 and an isolated amorphous carbon nanopipe (ACNP). The results indicate that the ions of the ILs form different layers inside these nanomaterials and their dynamics are slower due to the confinement. We also found significant differences in the densities and mobilities of ions caused by pore morphologies. Moreover, the presence of IL adsorbed in the outer surface of an uncharged ACNP in CMK-5 affects the dynamics and the density of an IL adsorbed inside the ACNP, and vice versa. Biased MD simulations have been performed to study the homogeneous nucleation of IL [dmim+][Cl-] from its supercooled liquid in the bulk, as well as the heterogeneous nucleation of the same IL near a graphitic surface. The string method in collective variables (SMCV) and Markovian milestoning with Voronoi tessellations, when used in combination with suitable order parameters proposed for molecular crystals, allow us to sketch a minimum free energy path (MFEP) connecting the supercooled liquid and crystal phases, and to determine the free energy and the rates involving in the nucleation processes. The physical significance of the configurations found along these MFEPs is discussed with the help of calculations based on classical nucleation theory, as well as simulation snapshots. Analogies and differences between both nucleation processes are analyzed and discussed. The simulation work described here is relevant to using ILs as electrolytes in energy-related devices, such as electrochemical double layer capacitors and dye-sensitized solar cells. Furthermore, nucleation of ILs is relevant to developing nanomaterials based on ILs

Studies of Structural and Chemical Ordering in Metallic Liquids and Glasses Using Electrostatic Levitation

Since the discovery of the first metallic glass in 1960, there has been a large research effort dedicated to understanding the glass transition and the formation of metallic glass from the supercooled liquid state. Knowledge of the relationship between the liquid\u27s structure and its thermophysical and kinetic properties provide insight into why some metallic alloy liquids form glasses more easily than others. Such structure and property measurements of high temperature, highly reactive metallic liquids in both their equilibrium and metastable, supercooled states are made possible through the use of the electrostatic levitation (ESL) technique. Presented here are the results of in situ high-energy X-ray scattering studies of metallic liquids and glasses utilizing the Washington University Beamline Electrostatic Levitation (WU-BESL) facility. Structural studies of binary Cu-Zr and Cu-Hf bulk glass-forming liquids and glasses reveal signatures of chemical ordering in the liquid with decreasing temperature and evidence for accelerated ordering in the deeply supercooled state. Novel experimental measurements and Reverse Monte Carlo simulations of the structure of bulk glass-forming Pd82Si18 liquid show a lack of acceleration in ordering, in contrast with the behavior of the widely studied Cu-Zr binary alloy liquids. Measurements of the liquid structures of Si-containing alloys (Au81Si19, Pd82Si18, Ni75Si25, and Pd77Cu6Si17) reveal a variety of chemical and topological signatures that may provide insight into differences in their glass-forming ability. More specifically, a signature of kinetic strength in structures of the Pd77Cu6Si17 liquid and glass support previous results while leading to a prediction of the structural behavior of the deeply supercooled Pd82Si18 liquid. In addition, the development of and first results from of a new ESL facility for complimentary neutron diffraction studies for use at the Spallation Neutron Source are also described