Die überraschende Entdeckung von ferroelektrischem Hafniumoxid durch Böscke et al. im Jahre 2011 eröffnet zahlreich technologische Möglichkeiten wie zum Beispiel voll CMOS kompatible ferroelektrische RAM Speicherzellen. Als kristallographische Ursache für dieses Verhalten erwies sich die Raumgruppe Pca21. In theoretischen Untersuchungen mit Hilfe der Dichtefunktionaltheorie erwies sich diese Phase jedoch als thermodynamisch instabil. Ziel dieser Dissertation ist daher zu klären, wie diese Phase stabilisiert werden kann. Dazu werden Faktoren wie Stöchiometrie, Temperatur, Druck, Spannung, Grenzflächenenergie sowie Defekte und Dotierung mit Hilfe der Dichtefunktionaltheorie untersucht. Die errechneten Ergebnisse werden mit Hilfe von Modellen interpretiert, welche im laufe dieser Dissertation erarbeitet werden. Es zeigt sich, dass neben dem energetischen Zustand auch der Herstellungsprozess des Materials eine bedeutende Rolle in der Stabilisierung der ferroelektrischen Phase von Hafniumoxid spielt. Abschließend wird versucht Verbindung zum Experiment herzustellen, in dem experimentell zugängliche Stellschrauben aufgezeigt werden, welche die ferroelektrischen Eingenschaften von Hafniumoxid verbessern können und sich aus den erarbeiteten Ergebnissen ableiten. / The surprising discovery of ferroelectric hafnium oxide by Böscke et al. in 2011 enables various technological possibilities like CMOS compatible ferroelectric RAM devices. The space group Pca21 was identified as the crystallographic cause of this behavior. However, this phase was proved to be thermodynamically unstable by several theoretical studies using density functional theory. Therefore, the goal of this dissertation is to investigate physical effects contributing to the stabilization of the ferroelectric phase by means of density functional theory. These effects include stoichiometry, temperature, stress, strain, interface energy, as well as defects and dopants. The computational results will be interpreted with models, which will be developed within this dissertation. It will become apparent, that in addition to the energetic state, the production process of a sample plays an important role in the stabilization of the ferroelectric phase of hafnium oxide. In the conclusion, this work will attempt to find a connection to the experiment, by identifying experimentally accessible parameters within the computational results which can be used to optimize the ferroelectric properties of ferroelectric materials.

<div> <div> <div> <p>The Effective Fragment Potential (EFP) is a quantum-mechanical based model potential for accurate calculations of non-covalent interactions between molecules. It can be coupled with ab initio methods in so-called QM/EFP models to explore the electronic properties of extended molecular systems by providing rigorous description of surrounding environments. The current EFP formulation is, however, not well suited for large-scale simulations due to its inherent limitation of representing effective fragments as rigid structures. The process of utilizing EFP method for the molecular systems with flexible degrees of freedom entails multiple sets of parameter calculations requiring intensive computational resources. This work presents development of the EFP method for describing flexible molecular systems, so-called Flexible EFP. To validate the applicability of the Flexible EFP method, extensive benchmark studies on the amino acid interactions, binding energies, and electronic properties of flavin chromophore of the cryptochrome protein have been demonstrated. In addition to methodological developments, excitonic properties of the Fenna-Matthews-Olson (FMO) photosynthetic pigment-protein complex are explored. In biological systems where intermolecular interactions span a broad range from non-polar to polar and ionic forces, EFP is superior to the classical force fields. In the present study, we demonstrate excellent performance of the QM/EFP model for predicting excitonic interactions and spectral characteristics of the FMO wildtype complex. We characterize the key factors for accurate modeling of electronic properties of bacteriochlrophyll a (BChl a) photosynthetic pigments and suggest a robust computational protocol that can be applied for modeling other photosynthetic systems. Developed computational procedures were also successfully utilized to elucidate photostability and triplet dynamics in the FMO complex and spectroscopic effects of single-point mutagenesis in FMO. A combination of polarizable EFP molecular dynamics and QM/EFP vibrational frequency calculations were also applied to understanding and interpreting structures and Raman spectroscopy of tert-butyl alcohol solutions. </p> </div> </div> </div>

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One learning problem is that public understanding of science is limited. Many people blame at least part of the problem on the predominant lecture approach for students' lack of science understanding. Current research indicates that more active instructional approaches can improve student learning in introductory undergraduate biology courses. Active learning may be difficult to implement because methods and strategies, ranging from in-class collaborative problem-solving to out of class multimedia presentations, are diverse, and sometimes difficult to implement. Merrill's First Principles of Instruction (hereafter referred to as "First Principles" or "First Principles of Instruction") provides a framework for implementing active learning strategies. This study used First Principles of Instruction as a framework for organizing multiple active learning strategies in a web-based module in an introductory biology course. Participants in this exploratory study were university students in Life Sciences 1350, an introductory biology course for nonscience majors. Students were randomly assigned to use either the module using First Principles of Instruction (hereafter called the First Principles module) or the module using a more traditional web-based approach (hereafter called the traditional module) as supplementary instruction. The First Principles module implemented several active learning strategies and used a progression of whole problems and several demonstration and application activities to teach the topic of "microevolution," defined as the study of how populations evolve and change over time. The traditional module implemented a more traditional web-based approach, providing information and explanations about microevolution with limited examples. This exploratory study's results showed that the learning gain from pretest to posttest at the remember level was significant for the traditional group at alpha = .05 and was significant for the First Principles group at alpha = .1. In addition the pretest to posttest gain at problem solving for the First Principles group was significant at alpha = .05. When students rated their confidence in solving future problems, those in the First Principles group were significantly more likely to predict future success at alpha = .1.

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Silicon nanowires (SiNWs) and the copper chalcogenides, namely copper sulfide (Cu2S) and selenide Cu2Se, have diverse applications in renewable energy technology. For example, SiNWs which have direct band gaps unlike bulk Si, have the potential to radically reduce the cost of Si based photovoltaic cells. However, they degrade quickly under ambient conditions. Various surface passivations have therefore been investigated for enhancing their stability but it is not yet well understood how they affect the electronic structure of SiNWs at a fundamental level. Here, we will explore, from first-principles simulation, how fluorine, methyl and hydrogen surface passivations alter the electronic structures of [111] and [110] SiNWs via strain and quantum confinement. We also show how electronic charge states in [111] and [110] SiNWs can be effectively modelled by simple quantum wells. In addition, we address the issue of why [111] SiNWs are less influenced by their surface passivation than [110] SiNWs. Like SiNWs, Cu2S and Cu2Se also make excellent photovoltaic cells. However, they are most well known for their exceptional thermoelectric performance. This is by virtue of their even more unique solid-liquid hybrid nature which combines the low thermal conductivity and good electrical characteristics required for a high thermoelectric efficiency. We use first-principles molecular dynamics simulations to show that Cu diffusion rates in Cu2S and Cu2Se can be as high as 10-5cm2s-1. We also relate their phonon power spectra to their low thermal conductivities. Furthermore, we evaluate the thermoelectric properties of Cu2S and Cu2Se using a combination of Boltzmann transport theory and first-principles electronic structure calculations. Our results show that both Cu2S and Cu2Se are capable of maintaining high Seebeck coefficients in excess of 200μVK-1 for hole concentrations as high as 3x1020cm-3.

Le but de ce mémoire est d’expliciter en détail et de voir la portée d'un passage bien précis du traité des Topiques, ouvrage où Aristote tente d'élaborer une méthode qui permettra de raisonner de manière dialectique. Dans le deuxième chapitre du premier livre (I, 2), il énonce de manière succincte trois utilités que le traité en question peut procurer à celui qui possède et maîtrise adéquatement cette méthode. En premier lieu, la dialectique servirait de gymnastique intellectuelle pour former l'esprit et lui donner plus de souplesse dans ses raisonnements. Dans un second temps, elle serait utile dans les rencontres de tous les jours avec autrui parce qu’elle permettrait de discuter et d'argumenter sur un sujet donné avec le premier venu. Enfin, il semble également que la dialectique soit utile pour les «connaissances de caractère philosophique», en ce sens qu'elle permettrait de développer les apories et ultimement, d'établir les principes ou les notions premières de chaque science. Dans ce travail, je me propose donc d’examiner chacune de ces prétendues utilités afin de voir comment, et dans quelle mesure, nous pouvons réellement affirmer que la dialectique s’avère profitable pour chacun des services énumérés en Topiques I, 2. / The purpose of this dissertation is to explain in detail the importance of a very precise passage of the Topics, treatise where Aristotle tries to find a method which will allow to reason in a dialectical way. In the second chapter of the first book (I, 2), he expresses in a brief way three utilities that the treatise in question can provide to those who own and control this method properly. First of all, the dialectic would serve as a mental gymnastic to train the mind and give it more flexibility in its reasoning. Secondly, it would be useful in the everyday encounters with others, because it would allow to discuss and argue on any given subject with the first person we could meet. Finally, it also seems that the dialectic would be useful for the "philosophical knowledge ", in the sense that it would go through the puzzles and ultimately, would establish the first principles of each science. In this work, I thus suggest examining each of its claimed utilities to see how, and in which measures, we can really assert that the dialectic turns out profitable for each of the services enumerated in Topics I, 2.

<p>The solid oxide fuel cell (SOFC) technology has been under research since thelate 1950s, and most of the research has been on designs utilizing yttria stabilized zirconia (YSZ) as the electrolyte of choice. However, the SOFC technology has the major drawback of requiring high operation temperatures (up to 1000 degrees Celcius), so research of alternative materials have come into interest that would possibly require a lower working temperature without any significant loss of conductivity.One such material of interest for the electrolyte is compounds of ceriumdioxide (ceria). Ceria is well known for its ability to release oxygen by formingoxygen vacancies under oxygen-poor conditions, which increases its oxygen ionconductivity, and works at a lower temperature than the YSZ compounds whenproperly doped. Conversely, ceria is also able to absorb oxygen under oxygen-rich conditions, and those two abilities make it a very good material to use in catalytic converters for reduction of carbon monoxide and nitrogen oxide emission. The ability for the oxygen ions to easily relocate inbetween the different lattice sites is likely the key property of oxygen ion transportation in ceria. Also, in oxygen-rich conditions, the absorbed oxygen atom is assumed to join the structure at either the roomy octrahedral sites, or the vacant tetrahedral sites. Following that, the oxygen atom may relocate to other vacant locations, given it can overcome a possible potential barrier.</p><p>This thesis studies how those interstitial oxygen vacancies (defects) affect theenergy profile of ceria-based supercells by first principles calculations. The system is modeled within the density functional theory (DFT) with aid of (extended) local density approximation (LDA+U) using the software VASP. Furthermore, it is studied how those vacancies affect neighbouring oxygen atoms, and wether or not it is energetically benificial for the neighbouring atoms to readjust their positions closer or further away from the vacancy. The purpose of this thesis is to analyze wether or not it is theoretically possible that interstitial oxygen vacancies may cause neighbouring oxygen atoms to naturally relocate to the octahedral site in ceria, and how this affects the overall energy profile of the material.</p>