Les nanofils semiconducteurs suscitent un vif intérêt tant pour leurs propriétés fondamentales originales que pour leurs applications potentielles en opto- et nano-Électronique. La physique des nanofils et en particulier des matériaux à la base est difficile à caractériser. Dans ce contexte, la simulation numérique peut apporter des réponses quantitatives aux problèmes posés par ces objets et aider à explorer leur potentiel. En particulier, leur cristallisation se fait dans une phase hexagonale wurtzite mais avec des fautes d’empilement qui donnent lieu à des insertions de séquence cubique. La structure cubique blende de zinc a été largement étudiée, les différents aspects physiques des semiconducteurs l’adoptant sont bien illustrés dans la littérature. Par contre, ils sont mal compris en phase wurtzite. C’est pourquoi, l’étude des propriétés structurales et électroniques des cristaux III-V et hétérostructures wurtzite a fait l’objet du présent travail. En particulier, je me suis intéressée à déterminer les paramètres structuraux et électroniques d’ InAs et InP. Pour aborder ces problématiques il convient de trouver une méthode théorique adaptée. Dans ce contexte, les modélisations ab initio permettent d’explorer les propriétés globales sans une connaissance expérimentale à priori des systèmes étudiés. Elles reposent sur la résolution variationnelle de l’équation de Schrödinger qui est lourde d’un point de vue computationnel. Il existe donc toute une hiérarchie de modèles plus ou moins sophistiqués qui approchent plus ou moins la solution exacte du problème. Dans le cadre de ce travail, j’ai utilisé la théorie de la fonctionnelle de la densité qui reproduit les résultats expérimentaux de structures mais peine à évaluer les niveaux énergétiques vides. Cette difficulté est due à la définition des effets à N corps et notamment aux effets de corrélation entre les électrons. L’erreur dans l’évaluation des énergies est corrigée grâce à la correction apportée par l’approximation GW ou les fonctionnelles hybrides. Ainsi, j’ai pu obtenir des structures électroniques correctes et exploitables afin de déterminer les potentiels de déformation. Il est notamment possible de faire varier la composition des nanofils de long de leur axe de croissance afin d’y introduire des jonctions p-N, des boîtes quantiques ou des barrières tunnel. Ces hétérostructures offrent de multiples opportunités : la faisabilité de transistors, de diodes à effet tunnel résonant ou de dispositifs à un électron basés sur les nanofils de silicium ou de III-V a ainsi déjà été démontrée. Ces matériaux permettent de réaliser des hétérostructures inédites car ils peuvent s’accommoder de forts désaccords de maille en déformant leur surface. La relaxation des contraintes structurales a toutefois un impact important sur leurs propriétés électroniques et optiques. Un des paramètres importants pour bien comprendre le comportement de ces structures quantiques est l’offset électronique ou la discontinuité énergétique. Il a été calculé pour le système InAs/InP et confronté à des études expérimentales suivant les directions de croissance. / Semiconductor nanowires are attracting much attention both for their original properties and their potential applications in opto- and nanoelectronics. The physics of nanowires and in particular materials at the base is poorly understood and difficult to characterize. In this context, the numerical simulation can provide quantitative answers to the problems posed by these objects and help to explore their potential. In particular, their crystallization is in a wurtzite (WZ) hexagonal phase but with stacking faults that result in insertions of cubic sequences. The zinc blende structure has been widely studied; the various structural, electronic and optical properties of semiconductor materials adopting this structure are well illustrated and discussed in the literature. On the other side, these properties are poorly understood for WZ. Study of WZ III-V materials and related heterostructures is the subject of this work. In particular, I have simulated the structural and electronic properties of relaxed InAs and InP and under strain condition. ab initio modeling or first principle may explore structural, electronic and dynamics of matter without any experimental prior knowledge. Here, DFT calculations are performed to model the structural and electronic properties of WZ InAs and InP. The error in the evaluation of conduction energy states has been circumvented with the use of GW approximation and hybrid functionals. Finally, I have studied band offset alignment and polarizations effects in InAs/InP WZ system.

Density functional theory has been used in combination with the correlation consistent and polarization consistent basis sets to investigate the structures and energetics for a series of first-row closed shell and several second-row molecules of potential importance in atmospheric chemistry. The impact of basis set choice upon molecular description has been examined, and irregular convergence of molecular properties with respect to increasing basis set size for several functionals and molecules has been observed. The possible reasons and solutions for this unexpected behavior including the effect of contraction and uncontraction, of the basis set diffuse sp basis functions, basis set superposition error (BSSE) and core-valence sets also have been examined.

In this research the validity of various computational techniques has been determined and applied the appropriate techniques to investigate and propose a good catalytic system for C-H bond activation and functionalization. Methane being least reactive and major component of natural gas, its activation and conversion to functionalized products is of great scientific and economic interest in pure and applied chemistry. Thus C-H activation followed by C-C/C-X functionalization became crux of the synthesis. DFT (density functional theory) methods are well suited to determine the thermodynamic as well as kinetic factors of a reaction. The obtained results are helpful to industrial catalysis and experimental chemistry with additional information: since C-X (X = halogens) bond cleavage is important in many metal catalyzed organic syntheses, the results obtained in this research helps in determining the selectivity (kinetic or thermodynamic) advantage. When C-P bond activation is considered, results from chapter 3 indicated that C-X activation barrier is lower than C-H activation barrier. The results obtained from DFT calculations not only gave a good support to the experimental results and verified the experimentally demonstrated Ni-atom transfer mechanism from Ni=E (E = CH2, NH, PH) activating complex to ethylene to form three-membered ring products but also validated the application of late transition metal complexes in respective process. Results obtained supported the argument that increase in metal coordination and electronic spin state increases catalytic activity of FeIII-imido complexes. These results not only encouraged the fact that DFT and multi-layer ONIOM methods are good to determine geometry and thermodynamics of meta-stable chemical complexes, but also gave a great support to spectroscopic calculations like NMR and Mossbauer calculations.

Orientador: Douglas Soares Galvão / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-24T13:39:40Z (GMT). No. of bitstreams: 1 Brunetto_Gustavo_D.pdf: 74304248 bytes, checksum: 1625a1a5cf52fb8ae1bd558d68118c27 (MD5) Previous issue date: 2014 / Resumo: Nas últimas décadas, sucessivas descobertas em materiais baseados em carbono abriram uma nova era na ciência dos materiais. Exemplos destas descobertas são os fulerenos, nanotubos de carbono e, mais recentemente, o grafeno. O grafeno é uma rede bi-dimensional de unidades hexagonais de carbono com ligações do tipo sp2. Grafeno apresenta propriedades mecânicas e eletrônicas não usuais e muito interessantes e devido a estas propriedades é um dos materiais mais promissores para aplicações em diversas áreas da tecnologia tais como eletrônica, militar, aeroespa- cial, dispositivos e outras. Entretanto, há algumas barreiras que devem ser superadas a fim de utilizar o grafeno em aplicações práticas. O grafeno, em sua forma pura, é um semicondutor com gap zero. Esta característica impõe sérias limitações em algumas aplicações em eletrônica, tal como, transistores. Além do mais, é muito difícil a síntese de grandes porções de grafeno que possuam poucos ou nenhum defeito estrutural. Através de simulações de primeiros princípios, propomos uma rota de síntese a partir da de-hidrogenação completa do grafeno poroso para a obtenção de um alótropo de carbono conhecido como BPC. Cálculos de estrutura eletrônica mostraram que o BPC possui um gap da ordem de 0,8 eV e orbitais de fronteira delocalizados, que exercem papel fundamental na mobilidade eletrônica do material. Na área de propriedades mecânicas, estudamos a impermeabilidade de membra- nas de grafeno. Quando depositadas sobre uma cavidade existente em uma superfície de óxido de silício. A membrana é mantida aderida sobre a superfície somente através da interação de van der Waals, entre os átomos da borda da membrana e do substrato. Inicialmente, confinado dentro da cavidade, há um gás (argônio ou hélio) e através de estudos de dinâmica molecular clássica, estudamos o mecanismo envolvido para a re- tenção e o vazamento do gás. Observamos que o gás não é capaz de vazar através da estrutura da membrana e determinamos as condições de pressão para que a membrana se descole da superfície e o gás seja liberado. O comportamento cadeias lineares de carbono confinadas dentro de nanotu- bos de carbono sujeitos a pressões extremamente altas foi analisado. Experimentos de Raman mostram uma diminuição na frequência de vibração das cadeias após todo o sistema ser submetido a altas pressões. Utilizamos o formalismo de campos de força reativo (ReaxFF) para entender a origem da diminuição das frequências de vibração da cadeia. Observamos que após a compressão ocorre uma ligação química entre a ex- tremidade da cadeia e a parede do nanotubo, que se mantém estável mesmo após a diminuição da pressão. Com a reação entre o nanotubo e a cadeia a interação entre alguns átomos da cadeia é alterada causando o enfraquecimento de algumas ligações. Através de cálculos do espectro vibracional, fomos capazes de identificar uma diminui- ção de intensidade no pico de vibração característico da cadeia e o aparecimento de um novo sinal em frequências menores. Além de estudar propriedades de materiais baseados em carbono, estudamos a possibilidade de se alterar o espectro de absorção ótico em moléculas através da uti- lização de fontes externas de laser. Devido a uma grande evolução na área de laseres ultra-rápidos, tornou-se possível estudar e caracterizar o movimento eletrônico durante um processo de excitação, por exemplo. Utilizamos a Teoria do Funcional Densidade Dependente do Tempo (TDDFT) para estudar como o espectro de absorção de molécu- las simples, como hélio e etileno, é alterado durante a interação destas moléculas com uma fonte intensa de laser. Observamos que há o aparecimento de um pico de absorção na região de gap ótico. Utilizamos técnicas de simulação computacional para estudar propriedades de diferentes tipos de sistemas. Para a membrana de grafeno, mostramos que esta é imper- meável aos gases considerados e quais os valores de pressão necessários para desprender a membrana do substrato quando esta é utilizada para selar uma cavidade que possui uma certa quantidade de gás confinado em seu interior. Com relação ao grafeno poroso, mostramos que após a completa remoção dos hidrogênios há uma interconverção para o BPC. Quanto à alteração na frequência de vibração das cadeias lineares de carbono dentro de nanotubos, mostramos que a pressão externa induz a formação de uma ligação química entre a cadeia e a parede do tubo, alterando a ligação entre alguns átomos da cadeia. Esta alteração causa uma diminuição na frequência de vibração dos átomos da cadeia. Por fim, através da metodologia de TDDFT, mostramos a alteração no espectro de absorção, devido a interação entre a amostra e um laser externo intenso / Abstract: In the last decades, successive discoveries in carbon-based materials have opened up a new era in materials science. Examples of these findings are fullerenes, carbon nanotubes, and more recently, graphene. Graphene is a two-dimensional hexagonal array of sp2-bonded carbon atoms. Graphene shows very interesting and unusual mechanical and electronic properties. Due to these special properties graphene is considered one of the most promising materials for applications in diverse areas such as electronics, military, aerospace, and other de- vices. However, there are obstacles that must be overcome in order to use graphene in practical applications. Graphene, in its pure form, is a zero-gap semiconductor. This feature imposes serious limitations in some applications in electronics, such as transis- tors. Moreover, it is very difficult to synthesize large portions of graphene that possess little or no structural defect. In this work, using first principle simulations, we propose a synthesis route from the complete dehydrogenation of porous graphene to obtain an carbon allotrope known as BPC. Electronic structure calculations show that the BPC has a band gap of 0, 8 eV and delocalized frontier orbitals, which has a primary role in material electronic mobility. In mechanical properties area, we studied the impermeability properties of graphene membranes. Graphene membranes were deposited over an existing cavity in a silicon oxide surface. The membrane is kept clamped on the surface only due to van der Waals interaction between the membrane edge atoms and the surface. Initially confined inside the cavity, there is a gas (argon or helium). We carried out classical molecular dynamics simulations in order to study the mechanism involved for the gas leakage. We observed that gas can not pass through the membrane structure and the leakage occurs only when membrane peel off the surface due to the gas high pressure inside the cavity. The behavior of carbon linear chains confined inside carbon nanotubes under extremely high pressure was considered. Experiments show a reduction in the Raman vibrational frequency of the chains after the entire system being subjected to high pressures. We use the formalism of reactive force fields (ReaxFF) to understand the origin of the chain vibrational frequency decrease. We observed that after compression a chemical bond between the end of the chain and the tube walls occurs, and remains stable even after lowering the pressure. The reaction between the nanotube and the chain causes the weakening of some connections between chain atoms. Through calcu- lated vibrational spectrum, we were able to identify a intensity decrease at the peak of characteristic vibration of the chain and the appearance of a new signal at lower frequencies. Besides studying properties of carbon-based materials, we studied the possibil- ity of modifying the optical absorption spectrum of molecules through external laser sources. Due to a great evolution in the area of ultrafast lasers, it has become possible study and characterize the electronic motion during an excitation process, for example. We use the Time-Dependent Density Functional Theory (TDDFT) to study how the absorption spectrum of single molecules such as helium and ethylene changes during due to the action of an intense laser source. We note that there is an appearance of an absorption peak in the optical gap region. We used computer simulation techniques to study properties of different system types. For the graphene membrane, we showed that it is impermeable to the considered gases and which pressure values is necessary to detach membrane from the substrate when it is used to seal a cavity with a certain amount of gas confined. With respect to porous graphene, we showed that after complete hydrogens removal there is an inter- conversion for BPC. Regarding the change in the vibrational frequency of linear carbon chains inside nanotubes, we showed that external pressure induces the formation of a chemical bond between chain and the tube, changing the weakening the bond between some chain atoms. This modification causes a decrease in the vibrational frequency. Finally, through the TDDFT methodology, we showed the change in the absorption spectrum, due to the interaction between the sample and an intense external laser field / Doutorado / Física / Doutor em Ciências

The focus of this thesis is on C-O bonds activation by transition metal atoms. Lignin is a potential alternative energy resource, but currently is an underused biomass species because of its highly branched structure. To aid in better understanding this species, the oxidative cleavage of the Cβ-O bond in an archetypal arylglycerol β-aryl ether (β–O–4 Linkage) model compound of lignin with late 3d, 4d, and 5d metals was investigated. Methoxyethane was utilized as a model molecule to study the activation of the C-O bond. Binding enthalpies (ΔHb), enthalpy formations (ΔH) and activation enthalpies (ΔH‡) have been studied at 298K to learn the energetic properties in the C-O bond cleavage in methoxyethane. Density functional theory (DFT) has become a common choice for the transition metal containing systems. It is important to select suitable functionals for the target reactions, especially for systems with degeneracies that lead to static correlation effects. A set of 26 density functionals including eight GGA, six meta-GGA, six hybrid-GGA, and six hybrid-meta-GGA were applied in order to investigate the performance of different types of density functionals for transition metal catalyzed C-O bond cleavage. A CR-CCSD(T)/aug-cc-pVTZ was used to calibrate the performance of different density functionals.

Despite the growing applications of silver nanoparticles, toxicity information on this nanomaterial is still deficient. Conclusions on the toxicity of silver nanoparticles vary and atomic level toxicity mechanisms are not yet achieved. Consequently, our group conducted combined computational and experimental toxicity studies of silver nanoparticles (AgNPs). Toxicity of 10 nm citrate stabilized AgNPs on HepG2 cells were investigated. Experimental results show that the 10 nm citrate stabilized AgNPs begin to be toxic to HepG2 cells at a dosage that exceeds 1 ppm and LD50 was observed at 3 ppm. Elevated reactive oxygen species levels were seen upon exposure to AgNPs with the maximum at the LD50 concentration of 3 ppm. Normal protein regulation of HepG2 cells were affected by exposure to AgNPs. TEM images of HepG2 cells exposed to AgNPs reveal that AgNPs can penetrate and agglomerate inside the cells. Our preliminary computational study was guided by one of the widely accepted toxicity mechanism of AgNPs in which the nanoparticles dissolute to Ag+. The computational model was composed of a 1:1 ratio of silver and phospholipid head. The silver employed are in atomic and anionic form while the phospholipid head are the phosphocholine (PC) and phosphoethanolamine (PE), which are abundant in HepG2 cells. Computational study shows that the presence of Ag+ results in partial oxidation of both the phospholipid heads. Our preliminary experimental and computational studies lead us to develop new computational methods that can accurately predict oxidation potentials (HOMO), reduction potentials (LUMO), and absorption spectra that can be used in studying toxicity mechanism of AgNPs through the oxidation pathway. Thus, computational methods for cyclic voltammetry and absorption spectroscopy that use DFT and TD-DFT, respectively, were improved to provide more accurate electronic and optical properties. Cyclopenta-fused polycyclic hydrocarbons (CP-PAHs) with available experimental data for HOMO, LUMO, ΔEgap and absorption spectra and have potential application as AgNP stabilizers were used in developing the improved computational methods for cyclic voltammetry and absorption spectroscopy. The improved computational method for cyclic voltammetry was developed by accounting for the anion species that occur experimentally and by using B3LYP the best density functional in predicting the HOMO, LUMO and ΔEgap of CP-PAHs with overall MAE of 014 eV. The best absorption spectra otef CP-PAHs were predicted using B3LYP for geometry optimizations followed by TD-CAMB3LYP with MAE of 29 nm. All calculations of CP-PAHs were implemented using the 6-311g (d,p) basis set and tetrahydrofuran (THF) as solvent. These two developed computational methods were tested on a group of methyl triphenyl amine (MTPA) derivatives with available experimental data for HOMO, LUMO, ΔEgap and absorption spectra and have potential application as AgNP stabilizers. The new computational methods for cyclic voltammetry and absorption spectroscopy also provided the most accurate predicted electronic and optical properties of MTPA derivatives. Among the ten density functionals employed, prediction of HOMO, LUMO and ΔEgap were most accurate using B3LYP and B3PW91 with overall MAE of 0.31 eV and 0.27 eV, respectively. Absorption spectra of MTPA derivatives were still best predicted using the B3LYP/TD-CAMB3LYP method with MAE of 13 nm. All calculations of MTPA were implemented using the 6-31+g (d,p) basis set and dichloromethane as solvent.

Density Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT can give good agreement with experiments. But moving to more sensitive properties like spin state energetic certain modifications of standard DFT are needed. First we investigated mixed ionic-electronic conducting perovskite type oxides with a general formula ABO3 (where A =Ba, Sr, Ca and B = Co, Fe, Mn). These oxides often have high mobility of the oxygen vacancies and exhibit strong ionic conductivity. They are key materials that find use in several energy related applications, including solid oxide fuel cell (SOFC), sensors, oxygen separation membranes, and catalysts. Different cations and oxygen vacancies ordering are examined using plane wave pseudopotential density functional theory. We find that cations are completely disordered, whereas oxygen vacancies exhibit a strong trend for aggregation in L-shaped trimer and square tetramer structure. On the basis of our results, we suggest a new explanation for BSCF phase stability. Instead of linear vacancy ordering, which must take place before the phase transition into brownmillerite structure, the oxygen vacancies in BSCF prefer to form the finite clusters and preserve the disordered cubic structure. This structural feature could be found only in the first-principles simulations and cannot be explained by the effect of the ionic radii alone. In order to understand vacancy clustering and phase iv stability in oxygen-deficient barium strontium cobalt iron oxide (BSCF), we predict stability and activation energies for oxygen vacancy migration. Using symmetry constrained search and Nudged Elastic Band method, we characterize the transition states for an oxygen anion moving into a nearby oxygen vacancy site that is surrounded by different cations and find the activation energies to vary in the range 30-50 kJ/mol in good agreement with experimental data. Next we study spin alignments of single molecule magnets (SMM). SMMs are a class of polynuclear transition metal complexes, which characterized by a large spin ground state and considerable negative anisotropy. These properties lead to a barrier for the reversal of magnetization. For these reasons SMM are expected to be promising materials for molecular spintronics and quantum computing applications. To design SMM for quantum computation, we need to accurately predict their magnetic properties. The most important property is, Heisenberg exchange coupling constant (J). This constant appears in model Heisenberg Hamiltonian that can be written in general form as here Jij represents the coupling between the two magnetic centers i and j with the spin states Si and Sj. The positive J values indicate the ferromagnetic ground state and the negative ones indicate the antiferromagnetic ground state. We found pure DFT is not accurate enough to predict J values. We employ density functionals with a Hubbard U term that helps to counteract the unphysical delocalization of electrons due to errors in pure exchange-correlation functionals. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to π-back bonding, inverting spin-polarization of the Jiij −= ∑ S.S.JH v acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect performance of the models assuming strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology for Mn12(mda) and Mn12(ada) complexes to calculate all six nearest neighbor Jij value. Our result shows both qualitative and quantitative agreement with experiments unlike other DFT studies. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single-molecule magnets for molecular spintronics and quantum computing applications. Finally we apply hybrid DFT methodology to calculate geometrical parameters for cerium oxides. We review the experimental and computational studies on the cerium oxide nanoparticles, as well as stoichiometric phases of bulk ceria. Electroneutral and nonpolar pentalayers are identified as building blocks of type A sesqioxide structure. The idealized structure of the nanoparticles is described as dioxide covered by a single pentalayer of sesquioxide, which explains the exceptional stability of subsurface vacancies in nanoceria. The density functional theory (DFT) predictions of the lattice parameters and bulk moduli for the Ce(IV) and Ce(III) oxides at the hybrid DFT level are also presented. The calculated values for both compounds agree with experiment and allow to predict changes in the lattice parameter with decreasing size of the nanoparticles. The results validate hybrid DFT as a promising method for future study the structure of oxygen vacancies and catalytic properties of ceria nanoparticles.

Quantum chemistry methodologies can be used to address a wide variety of chemical problems. Key to the success of quantum chemistry methodologies, however, is the selection of suitable methodologies for specific problems of interest, which often requires significant assessment. To gauge a number of methodologies, the utility of density functionals (BLYP, B97D, TPSS, M06L, PBE0, B3LYP, M06, and TPSSh) in predicting reaction energetics was examined for model studies of C-O bond activation of methoxyethane and methanol. These species provide excellent representative examples of lignin degradation via C-O bond cleavage. PBE0, which performed better than other considered DFT functionals, was used to investigate late 3d (Fe, Co, and Ni), 4d (Ru, Rh, and Pd), and 5d (Re, Os, and Ir) transition metal atom mediated Cβ -O bond activation of the β–O–4 linkage of lignin. Additionally, the impact of the choice of DFT functionals, basis sets, implicit solvation models, and layered quantum chemical methods (i.e., ONIOM, Our Own N-layered Integrated molecular Orbital and molecular Mechanics) was investigated for the prediction of pKa for a set of Ni-group metal hydrides (M = Ni, Pd, and Pt) in acetonitrile. These investigations have provided insight about the utility of a number of theoretical methods in the computation of thermodynamic properties of transition metal hydrides in solution. As single reference wavefunction methods commonly perform poorly in describing molecular systems that involve bond-breaking and forming or electronic near-degeneracies and are typically best described with computationally costly multireference wavefunction-based methods, it is imperative to a priori analyze the multireference character for molecular systems so that the proper methodology choice is applied. In this work, diagnostic criteria for assessing the multireference character of 4d transition metal-containing molecules was investigated. Four diagnostics were considered in this work, including the weight of the leading configuration of the CASSCF wavefunction, C02; T1, the Frobenius norm of the coupled cluster amplitude vector related to single excitations and D1, the matrix norm of the coupled cluster amplitude vector arising from coupled cluster calculations; and the percent total atomization energy, %TAE. This work demonstrated the need to have different diagnostic criteria for 4d molecules than for main group molecules.

Nuclear Magnetic Resonance (NMR) and computational methods increasingly play a predominant and indispensable role in modern chemical research. The insights into the local nuclear environment that NMR can provide is unique information which allows the structural characterization of novel materials, as well as the understanding and explanation of their relevant properties on an atomic scale. Computational methods, on the other hand, can be used to support experimental findings, providing a rigorous theoretical basis. Furthermore, when more complex chemical systems are considered, calculations can prove to be invaluable for the interpretation of experimental data and often allow an otherwise impossible spectral assignment. This thesis presents a series of studies in which NMR spectroscopy, in combination with computational methods, is utilized to investigate a variety of chemical systems both in solution and the solid state. An overview of the thesis and experimental and computational details are given in Chapter 1. In Chapter 2, the quantum mechanical basis necessary for the description of the NMR phenomenon is presented. Chapter 3 explores the main experimental techniques employed routinely for the acquisition of NMR spectra in both solution and the solid state. Chapter 4 describes the main features of density functional theory (DFT) and its implementation in computational methods for the calculation of relevant NMR parameters. Chapter 5 reports an experimental solution-phase NMR study and a parallel computational investigation of the poly(CTFE-co-EVE) fluoropolymer. In Chapter 6, the combination of [superscript(14/15)]N solution-phase NMR techniques and DFT methods for the study of alkylammonium cationic templates used in the synthesis of microporous materials is presented. The characterization of a boroxoaromatic compound in the solid state and the study of its reactivity are described in Chapter 7. In Chapter 8, two experimental NMR methods for the study of the anisotropic chemical shift interaction in the solid state are compared and used to characterize a range of materials. Cross-polarization and nutation of quadrupolar nuclei are computationally investigated under both static and spinning conditions in Chapter 9. A general conclusion and a summary are given in Chapter 10.

Thesis (PhD)--Stellenbosch University, 2013. / Please refer to full text to view abstract.