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Orientador: Augusto Batagin Neto / Resumo: Polímeros orgânicos conjugados são considerados materiais de grande relevância para aplicações tecnológicas variadas, principalmente devido às suas propriedades optoeletrônicas únicas e métodos utilizados em sua síntese. Nesse contexto, os derivados de polipirrol (PPy) têm sido amplamente empregados. A grande variabilidade de síntese desse material permite a produção de uma série de derivados com propriedades distintas, permitindo sua aplicação em diversas áreas. Neste trabalho, cálculos de estrutura eletrônica foram realizados para avaliar a influência de grupos laterais nas propriedades estruturais, ópticas, eletrônicas e de reatividade de derivados de PPy, em especial para aplicações como sensores químicos. Os cálculos foram feitos para sistemas oligoméricos aplicando a teoria do funcional da densidade. Estudos de preliminares foram conduzidos utilizando dois funcionais distintos para otimização de geometria e avaliação de propriedades optoeletrônicas. Estudos comparativos da alternância de comprimento de ligação, distribuição espacial e energética dos orbitais de fronteira, gaps eletrônicos, energias de ligação de éxcitons, espectros de absorção óptica, densidade eletrônica de estados e reatividade local foram conduzidos para cada derivado e a influência dos grupos laterais foi discutida em termos de suas propriedades de inserção/retirada de elétrons. Um conjunto de regras simples (equações lineares) foi proposto para a predição de propriedades optoeletrônicas de derivado... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Conjugated organic polymers have been considered interesting materials for varied technological applications, mainly due to their unique optoelectronic properties and variety of methods employed in their synthesis. In this context, polypyrrole (PPy) derivatives have been widely employed. The great versatility of synthesis of this material allows the production of a number of derivatives with distinct properties, allowing their application in several areas. In this report, aiming to guide the design of compounds with specific features, electronic structure calculations were conducted to evaluate the influence of side groups in the structural, optical and electronic properties of PPy derivatives, specially for application in chemical sensors. The calculations were carried out for oligomeric systems in the framework of the density functional theory. Preliminary benchmark studies were conducted by employing two distinct functionals for geometry optimization and evaluation of optoelectronic properties. Comparative studies of the bond length alternation, spatial and energetic distribution of the frontier orbitals, electronic gaps, exciton binding energies, optical absorption spectra, electronic density of states and local reactivity were conducted for each derivative and the influence of the side groups was discussed in terms of their electron donation/withdrawing properties. A set of simple rules (linear equations) was proposed for the prediction of optoelectronic properties of PP... (Complete abstract click electronic access below) / Mestre

Thesis is aimed at studying of magnetic iron oxide particles of submicron and nanoscale dimensions by means of nuclear magnetic resonance (NMR). 57 Fe NMR inves- tigations were carried out in composite bentonite/maghemite with respect to tempera- ture of calcination (Tcalc) during the sample preparation and in magnetite submicron powders with respect to various range of the particles size. One of the main findings is that increasing Tcalc improves resolution in the NMR spectra, which is most likely connected with higher degree of atomic ordering in the spinel structure. Evaluating the integral intensities of NMR spectra allowed us to determine the relative content of maghemite phase in particular samples of the series: the content rapidly grows for Tcalc up to ∼420 deg. An approach to distinguish signal from tetrahedral and octahedral irons was developed and tested on pure maghemite sample. Analysis based on vacancy- distribution models was performed in the spinel structure and the results were compared to the experiment. 57 Fe NMR spectra in submicron magnetite samples were found to differ markedly from spectrum of a single crystal. It was concluded that the investigated powders possess high amount of defects in the crystal structure or contain additional phase (probably closely related to the maghemite phase).

In this thesis, we summarize the material-specific theories of strongly correlated systems and apply them to selected materials. We describe and apply the corre- lated band theory methods: the local density approximation plus Coulomb U, and the density functional theory plus exact diagonalization of single impurity An- derson model. First, we investigate the systems containing impurity atoms: cobalt impurity located in the bulk copper and samarium, and neodymium adatoms on the surface of graphene. We present the spectral densities and study the magnetism of those compounds. Afterwards, we analyze three Np-based compounds: NpPt2In7, Np2Ni17 and NpBC. For all three compounds we analyze the spin, orbital and to- tal magnetic moments and the total density of states, as well as its projections for selected orbitals and spins. Moreover, for NpPt2In7 and NpBC we perform the to- tal energy analysis between different magnetic moment arrangements on the Np atoms.

In dieser Doktorarbeit wurde die elektronische Struktur von konventionellen und unkonventionellen Supraleitern untersucht. Das Ziel dieser Arbeit war es, die dHvA Parameter zu berechnen und mit experimentellen Daten zu vergleichen. Mit Hilfe des Bandstrukturprogrammes FPLO, welches auf der DFT basiert, untersuchten wir Diboride (MgB$_2$ und TaB$_2$) und schwere Fermionenverbindungen (CeMIn$_5$ und PuMGa$_5$, M=Co, Rh, und Ir) innerhalb der LSD-Näherung. / In this thesis theoretical study of the electronic structure of conventional and unconventional superconductor compounds was carried out. The goal was to calculate the dHvA parameters in comparison with available experimental data. By means of FPLO band structure code based on DFT within LSDA we investigated diborides (MgB$_2$ and TaB$_2$) and heavy fermion compounds (CeMIn$_5$ and PuMGa$_5$, M=Co, Rh, and Ir).

Accurate energetic modeling of large molecular systems is always desired by chemists. For example, ligand-protein binding simulations and enzymatic catalysis studies all involve with a small energy difference. The energetic accuracy depends largely on a proper handling of electronic correlations. Molecular mechanics (MM) methods deliver a parameterized Newtonian treatment to these problems. They show great capability in handling large calculations but give only qualitatively good results. Quantum mechanics (QM) methods solve Schrödinger equations and exhibit much better energy accuracy, though the computational cost can be prohibitive if directly applied to very large systems. Fragment-based methods have been developed to decompose large QM calculations into fragment calculations. However, most current schemes use a self- consistent field (SCF) method on fragments, in which no electronic correlation is accounted for. The super-system energy is computed as a sum of fragment energies plus two-body corrections and, possibly, three-body corrections (a "body" is a fragment). Higher order corrections can be added. Nevertheless, many problems require the treatment of high order electronic correlations. The coupled-cluster (CC) theory is the state-of-the-art QM method for handling electronic correlations. The CC wavefunction contains correlated excitations up to a given truncated level and coincidental excitations for all possible electronic excitations. It is a brilliant way of including more electronic correlations while maintaining a low-order scaling. In the proposed excitonic coupled-cluster (X-CC) theory, substantial modifications have been made to allow CC algorithms to act on the collective coordinates of fragment fluctuations to obtain super-system energy. The X-CC theory is designed to achieve accurate energetic modeling results for large chemical systems with much improved affordability and systematic improvability. The test system used in this work is a chain of beryllium atoms. A 30-fragment X-CCSD(2) calculation delivered matching accuracy with traditional CCSD method. An X-CCSD(2) calculation on a chain of 100 bonded fragments finished in 7 hours on a single 2.2 GHz CPU core. The X-CC scheme also demonstrates the ability in handling charge transfer problems. Due to the use of fluctuation basis in the test cases, the excitonic algorithms can be easily generalized to inhomogeneous systems. This will be investigated in future work.

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This thesis describes an accurate and scalable computational method designed to perform nanoelectronic structure calculations. Built around the FEAST framework, this method directly addresses the nonlinear eigenvalue problem. The new approach allows us to bypass traditional approximation techniques typically used for first-principle calculations. As a result, this method is able to take advantage of standard muffin-tin type domain decomposition techniques without being hindered by their perceived limitations. In addition to increased accuracy, this method also has the potential to take advantage of parallel processing for increased scalability. The Introduction presents the motivation behind the proposed method and gives an overview of what will be presented for this thesis. Chapter 1 explains how electronic structure calculations are currently performed, including an overview of Density Functional Theory and the advantages and disadvantages of various numerical techniques. Chapter 2 describes, in detail, the method proposed for this thesis, including mathematical justification, a matrix-level example, and a description of implementing the FEAST algorithm. Chapter 3 presents and discusses results from numerical experiments for Hydrogen and various Hydrogen molecules, Methane, Ethane, and Benzene. Chapter 4 concludes with a summary of the presented work and its impact in the field.

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<p> Working within the framework of the linearized Boltzmann equation for the conduction electrons the existing theoretical treatments of ultrasonic attenuation in metals are extended to include realistic descriptions of the electronic structure and electron-lattice interaction. A variational solution of the Boltzmann equation which allows the inclusion of phonon drag effects is derived. An anisotropic scattering time solution is also presented. Both of these solutions are applied to calculation of the attenuation coefficient in pure metals and dilute alloys. </p> <p> The theory of the effects of electron-electron collisions on the ultrasonic attenuation in metals is also examined. </p> / Thesis / Doctor of Philosophy (PhD)