It has been 10 years since the first hybrid halide perovskite photovoltaics was fabricated. Power conversion efficiency increases from the initial 3.8% to the current 25.2%. Fabrication method envolves from spin-coating to printable technology, and we deeply experience the drastic development of hybrid halide perovskite photovoltaics. Although hybrid halide photovoltaics render a variety of advantages over traditional photovoltaics, we still cannot find any practical application of these hybrid halide photovoltaics. There exist a few issues which hinder the commercialization of this type of solar cell. Among these issues, the long-term instability of hybrid halide perovskite is the main concern for the next development. This thesis expands on investigating the instability of hybrid halide perovskites from first principles. In Chapter 1, two computational methods employed in the thesis: density functional theory and Ab initio molecular dynamics are introduced. Theoretical investigations of the instability of CH3NH3PbI3 using density functional theory method are mainly conducted at 0 K. The finite temperature effect on this instability of CH3NH3PbI3 is usually neglected. In Chapter 2 of this thesis, we combined density functional calculations and additional thermodynamic data to explain the intrinsic instability of CH3NH3PbI3 under finite temperature conditions. We also analyzed the stability under humid conditions. It is shown that the aqueous solubilities of reactants play an important role in the products’ stabilities. The Born–Haber cycle of NaCl splits the enthalpy change into several components which will give a better understanding of the origin of the corresponding enthalpy change. In Chapter 3, with the extension of the Born–Haber cycle to the hybrid halide perovskites, the reaction enthalpies which govern the intrinsic instability of ionic compounds were analyzed. We proposed a criterion that helps to filter the hybrid halide perovskites with improved stability aimed for photovoltaics. Since the instability of CH3NH3PbI3 is intrinsic. The long-term instability can be settled by discovering alternative perovskite absorber. In Chapter 4, based on literature research, we propose a three-membered ring cation which has a suitable size to fit into the Pb-I framework, leading to optimal band gap for photovoltaics. Besides, the cation has a good ionization energy which will potentially render better stability. Whereas, a comprehensive study of this cyclic ring based perovskite indicates that the instability of the three-membered ring cation will make it impossible to synthesize this theoretical structure. Moisture degradation mechanisms of CH3NH3PbI3 are investigated intensively. More importantly, for practical photovoltaics, we have to imagine different situations the modules will encounter, e.g. after a couple of years, cracks appearing on the modules are inevitable, at this stage, understanding of the degradation mechanism of CH3NH3PbI3 according to liquid water becomes important. Chapter 6 elaborately describes a comprehensive degradation mechanism of CH3NH3PbI3 under liquid water. We investigate the energy barrier for the first dissolution event of CH3NH3PbI3 in water. Furthermore, thermodynamic analyses of CH3NH3PbI3 dissolution in water clearly explain the spontaneity of CH3NH3PbI3 degradation in water. Besides, different mechanisms of CH3NH3PbI3 and CsPbI3 dissolution in water are discussed. / Dissertation / Doctor of Philosophy (PhD)

Liquid mixture is everywhere in the chemical industry and widely studied by researchers. An accurate prediction of its physicochemical property is of vital importance in developing efficient process optimization. However, measurements from experiment are usually time consuming and inefficient. Furthermore, clear understanding of many of fundamental physicochemical phenomena hasn't been obtained, which restricts the development of novel products. Molecular simulation techniques have become an impressive tool to deal with these challenges during past decades. This thesis mainly applied molecular simulation to predict the physicochemical properties of industrially relevant mixtures and investigate the molecular mechanism behind observed phenomena. Among various properties, cohesive energy is the central focus, which reveals intermolecular interactions between molecules of different types. Mixture systems of two different areas of application were studied. The first is amorphous polymer-plasticizer mixtures, which, with varying composition, correspond to plastic products of different grades for application in different areas. The most important class of plasticizers are phthalate diesters, in which di (2-ethylhexyl) phthalate (DEHP) is the most frequently used compound. However, phthalates are prone to migration loss from the host poly(vinyl chloride) (PVC), which results in the contamination of surrounding environment, gradual deterioration of plastics performance, and potential harm to human health. It has thus prompted tightening governmental regulation on their usage. With this background, we aim to address three challenges: (I) model plasticized PVC to predict its physicochemical property, (II) obtain molecular insight into plasticization and plasticizer diffusion pattern inside PVC, (III) correlate plasticizer performance -- compatibility, efficacy, and mobility -- with its molecular structure. Cohesive energy plays a central role especially in understanding plasiticzer compatibility and migration tendency. Our modeling and simulation protocol is firstly tested on phthalates, where the simulated plasticization efficacy and thermodynamic compatibility with the host polymer agree well with all known experimental observations. Furthermore, through simulation of plasticizer diffusion pattern, we found relaxation of the alkyl side chains is a key factor in plasticizer migration. Next, we expand our simulation to a wider group of plasticizers including adipates, trimellitates, and citrates. The computed mixing enthalpy and Young's modulus again show an excellent agreement with available experimental data. Dependance of plasticizer performance on seven molecular design parameters are evaluated. The obtained relationship clearly tells us decreasing leg length or increasing branching on the leg will raise plasticizer compatibility with PVC, changing the torso group from benzene ring to alkane chain will highly improve plasticizer efficacy, and attaching three legs on the torso will decrease plasticizer mobility. As a side outcome, we also report a nontrivial chain-length dependence of the cohesive energy and solubility parameter of long-chain polymers, which is an important consideration in the calculation of these quantities using molecular simulation. The second area is azeotropes, the separation of which in chemical processes is usually very difficult due to the same composition in vapor and liquid phases at the azeotropic point. So far, a fundamental understanding of azeotrope formation is still missing. In this thesis, we aim to address two fundamental questions: (I) the mechanism for ethanol/benzene azeotrope formation, (II) classification of different polar-polar positive azeotropes. First, Gibbs ensemble Monte Carlo (GEMC) simulation is performed to predict the vapor-liquid equilibrium (VLE) phase diagram of ethanol/benzene, including an azeotrope point. The results match well with experiments. Free energy and cohesive energy profiles analyses are then performed. From a thorough liquid structure analysis, we conclude a three-stage mechanism for azeotrope formation: 1) formation of small ethanol clusters at low composition, 2) microscopic phase separation between ethanol and benzene, 3) isolation of benzene. This approach is then extended to four additional polar-polar mixtures (ethyl acetate/methanol, ethyl acetate/ethanol, ethanol/water, and 1-propanol/water) to obtain their VLE diagrams, which again match well with experiments. Free energy and cohesive energy analyses indicate that there are two types of mechanisms, a three-stage mechanism with weak cross-interactions (for the first two mixtures) and a three-stage mechanism with strong cross-interactions (for the last two mixtures). So far, our analyses on mixture liquid micro-structure can partially prove the existence and classification of those mechanisms. Overall, the successful prediction in physicochemical properties of two liquid mixtures with very different molecular scales proves the robustness of our study strategy, which could be used to study any liquid mixtures and understand their related physicochemical phenomena. / Thesis / Doctor of Philosophy (PhD)

No description available.

No / In this work, parameters of the steric mass-formalism SMA are optimally ascertained for a reliable determination of the adsorption isotherms of beta-lactoglobulin A and B under non-isocratic conditions. For this purpose, static batch experiments are used in contrast to the protocols based on different experimental steps, which use a chromatographic column. It is shown that parameters can already be determined for a small number of experiments by using a systematic procedure based on optimal model-based experimental design and an efficient NLP-solver. The in different works observed anti-Langmuir shape of the isotherm for small concentrations of beta-lactoglobulin A was corroborated. Moreover, we also found indications for a porosity variation with changing protein concentrations.

Alzheimer's disease is the leading cause of senile dementia in the elderly, and as life expectancy increases across the globe, incidence of the disease is continually increasing. Current estimates place the number of cases at 25-30 million worldwide, with more than 5.4 million of these occurring in the United States. While the exact cause of the disease remains a mystery, it has become clear that the amyloid β-peptide (Aβ) is central to disease pathogenesis. The aggregation and deposition of this peptide in the brain is known to give rise to the hallmark lesions associated with Alzheimer's disease, but its exact mechanism of toxicity remains largely uncharacterized. Molecular dynamics (MD) simulations have achieved great success in exploring molecular events with atomic resolution, predicting and explaining phenomena that are otherwise obscured from even the most sensitive experimental techniques. Due to the difficulty of obtaining high-quality structural data of Aβ and its toxic assemblies, MD simulations can be an especially useful tool in understanding the progression of Alzheimer's disease on a molecular level. The work contained herein describes the interactions of Aβ monomers and oligomers with lipid bilayers to understand the mechanism by which Aβ exerts its toxicity. Also explored is the mechanism by which flavonoid antioxidants may prevent Aβ self-association and destabilize toxic aggregates, providing insight into the chemical features that give rise to this therapeutic effect. / Ph. D.

Recent theoretical and numerical investigations revealed the prospect that the instantaneous total temperature is nonuniform around vortices. For low Mach number flows, the instantaneous total pressure was also shown to become nonuniform in such a similar manner that the near-wake patterns of instantaneous total pressure exhibit almost exact facsimiles of these of total temperature. Here, the time-accurate measurements of the fluctuating total temperature and pressure are presented by placing an aspirating probe in the vortex street behind a cylinder. The data, obtained at a uniform upstream Mach number of 0.4 and with the vortex street in its natural (unexcited) state, show a significant fluctuation of total temperature and pressure. In addition, their time-traces taken in the near-wake are qualitatively similar. / M.S.

Thermodynamic properties are calculated for mixtures of ideal gases in equilibrium for temperatures up to 15,000° K. Results for air and a model Mars atmosphere are given. The equilibrium composition of a gas mixture at a given temperature and pressure is determined by minimizing the Gibbs free energy. Species of the following types are included in the mixture: atoms and atomic ions, diatomic and linear triatomic molecules and ions, and electrons. Quantum statistical mechanics is used to determine thermodynamic properties of each species. For the diatomic species, accurate evaluations of vibrational anharmonicity, vibration-rotation interaction, and rotational stretching corrections are carried out. Comparisons are made between results with and without the above corrections. / Master of Science

A Dispersion model for ozone inside the rectangular duct of an indoor air quality pilot plant was simulated. Using this the concentration profiles of ozone at several points downstream of ozone insertion were simulated and they matched well with experimental results. Recommendations for future work are cited. A thermodynamic study was conducted to check the levels of concentration in which certain toxic compounds could be present due to the oxidation of pre-determined chlorinated compounds. STANJAN, a package which solves for equilibrium concentrations using the element potential method, was used. Recommendations for future work are cited. A Reaction model was developed for the global oxidation reactions occurring in the catalyst bed which is situated downstream of the ozone insertion. Once this was done, the effect of moisture and temperature were studied qualitatively and recommendations for further work are Cited. / Master of Science

Aqueous-polymer two-phase systems consist of various combinations of water, polymer(s), low molecular weight component(s), and salts. These aqueous-polymer systems are comprised of two phases, each of which contains about 90 percent (by weight) water. Due to some very unique properties, these systems have been applied to separations involving biological molecules for at least a quarter of a century. In particular, these systems are inexpensive, efficient, and provide a mild (aqueous) and possibly stabilizing environment for fragile biologically-active molecules. These systems may also be designed for a high degree of selectivity. Although much effort has been expended in the area of polymer solution theory, the theory of why these systems exhibit this extraordinary two-phase behavior that characterizes them as viable liquid-liquid extraction systems for use with biologically-active molecules is not completely understood. A thermodynamic model which could accurately represent the phase equilibria exhibited by these systems would be useful for the design of systems for use in many different applications. A potpourri of thermodynamic models and their underlying theoretical structure have been critically studied for their particular application to predicting the phase behavior of aqueouspolymer two-phase systems. In particular, the Flory-Huggins model is reviewed (with discussion of its inadequacies and subsequent modifications); the theory of Ogston; the model by Heil; several local composition models (NRTL, Wilson, and UNIQUAC); and two group-contribution models (ASOG and UNIFAC) are all discussed. The development of a solvent-electrolyte model (Chen's model) based on local composition theory (in particular the NRTL model) is reviewed, and the subsequent possible modification of this theory for solvent-polymer-electrolyte systems is discussed. The pros and cons of each model are discussed and qualitative results are given. Quantitative comparisons with experimental data are made with several of these models when appropriate data are available. The main conclusions of this work are: 1. A major limitation to the modeling of these aqueous-polymer two-phase systems is the lack of experimental data. Sufficient, accurate data is needed for the reduction of meaningful thermodynamic parameters by which thermodynamic models can be tested for their applicability. There exists a definite need for the generation of accurate, meaningful thermodynamic data from well characterized systems. 2. The most promising model identified in this work is the theory of Ogston. First, the model is based on the virial expansion and is thus quite suitable for dilute solutions. The Ogston model is the simplest theoretically-relevant dilute-solution model. Second, it appears to be easily extended to solvent-polymer-electrolyte solutions. 3. The Flory equation of state approach appears to be promising for representing polymer solutions. The free volume dissimilarity effect on which it is based is extremely important for solvent-polymer solutions. The most important aspect of this theory is its ability to predict lower critical solution temperature (LCST) behavior -- for which the Flory-Huggins theory is totally inadequate. / M.S.

Yes / In this article we briefly review the Boxed Molecular Dynamics (BXD) method, which allows analysis of thermodynamics and kinetics in complicated molecular systems. BXD is a multiscale technique, in which thermodynamics and long-time dynamics are recovered from a set of short-time simulations. In this article, we review previous applications of BXD to peptide cyclization, diamond etching, solution-phase organic reaction dynamics, and desorption of ions from self-assembled monolayers (SAMs). We also report preliminary results of simulations of diamond etching mechanisms and protein unfolding in AFM experiments. The latter demonstrate a correlation between the protein’s structural motifs and its potential of mean force (PMF). Simulations of these processes by standard molecular dynamics (MD) is typically not possible, since the experimental timescales are very long. However, BXD yields well-converged and physically meaningful results. Compared to other methods of accelerated MD, our BXD approach is very simple; it is easy to implement, and it provides an integrated approach for simultaneously obtaining both thermodynamics and kinetics. It also provides a strategy for obtaining statistically meaningful dynamical results in regions of configuration space that standard MD approaches would visit only very rarely. / DRG is grateful for funding from a Royal Society Research Fellowship. JB and DVS acknowledge the support of EPSRC (Grant No EP/E009824/1). E.M.-N. and S.A.V. are grateful to the “Centro de Supercomputación de Galicia (CESGA)” for the use of its computational resources, as well as to “Ministerio de Economía y Competitividad” (Grant No. CTQ2009-12588) for financial support. DS and E.M.-N. acknowledge the Leverhulme Trust for funding the E.M.-N. visit to Leeds by the grant “Accelerated classical and quantum molecular dynamics and its applications” (Grant No. VP1-2012-013).