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Les descriptions des interactions faibles et notamment de la dispersion représentent un problème majeur pour la théorie de la fonctionnelle de la densité. En effet, le caractère fortement local des fonctionnelles rend problématique la description des interactions à longue-portée. Aussi, plusieurs stratégies sont envisagées: des corrections des fonctionnelles existantes ou une introduction de méthodes post-Hartree-Fock par séparation de portée. Des résultats dans les deux cas sont exposés. Tout d'abord, la méthodologie hybride est appliquée à des dimères de métaux de transition (Cr2, Mn2 et Zn2). Ensuite, le calcul de coefficients de corrections pour la dispersion dans un cadre relativiste est présenté. Enfin, les interactions faibles peuvent également résulter de l'interaction d'une molécule avec un champ magnétique. Dans ce cadre, une modélisation de la modification de la densité électronique dans les systèmes aromatiques sous l'influence d'un champ magnétique extérieur est présentée. / In quantum chemistry description of weak interactions, and particularly dispersion forces, are major problems for density functional theory. The strongly local character of functional does not allow to describe properly the long range interactions. Thus, two different strategies have been considered. Correcting the available functional or introduce post-Hartree-Fock methods by mean of range separation.Results in the two cases are discussed. First, the range separated hybrid methodology is applied to transition metal dimers (Cr2, Mn2 and Zn2). Then, correction coefficients for dispersion are calculated within the relativistic framework. Within this relativistic framework, a modelling of the electronic density in aromatic system under the influence of an external magnetic field is also presented.

Acenes are a class of polycyclic aromatic hydrocarbons (PAH) with linearly fused benzene rings. They are widely considered as promising materials for organic and molecular electronics. However, larger molecules of this class possessing more than five rings are chemically extremely reactive and show a very low solubility. Hence, large acenes are difficult to handle, and the experimental data available to date is limited. The aim of this work is to show a very promising protocol of how acenes with different lengths can be stabilized and investigated on metallic surfaces. The experimental approach of on-surface synthesis is explored to generate the respective acenes directly on the metallic substrate via the reduction of suitable precursor molecules. High-resolution scanning probe microscopy (SPM) is employed at a temperature of 5 K to verify the chemical conversion at a single-molecule level. In the first part of this work, the on-surface synthesis of acenes is introduced via the example of tetracene (4-acene) formation on Cu(111). Precursors with 1,4-epoxy moieties preferably adsorb with their oxygen-rich site facing the substrate. Subsequently, they can be deoxygenated via annealing of the substrate or by single-molecule manipulation with the tip of the scanning probe microscope. In both cases, atomic force microscopy (AFM) measurements resolve the planar adsorption geometry of tetracene on the surface with atomic resolution. Based on these findings, scanning tunneling microscopy (STM) is employed to investigate the self-assembly patterns of on-surface generated anthracene (3-acene) and tetracene molecules after synthesis on Au(111). These measurements show intriguing organic nanostructures and supramolecular networks that can form at the metallic interface upon thermally-induced surface reactions. The second part of this thesis focuses on the electronic structure of acenes adsorbed on a metallic substrate. By applying the novel method of on-surface reduction, single and isolated hexacene (6-acene) molecules are investigated on Au(111). Scanning tunneling spectroscopy (STS) measurements indicate a weak interaction with the substrate and reveal five accessible molecular resonances at the organic-metal interface. The differential conductance maps with high spatial resolution at the respective resonant bias values compare well to elastic scattering quantum chemistry-based calculations. Finally, the experimental investigations of Br-substituted precursors show the stabilization of genuine unsubstituted heptacene (7-acene), as confirmed by imaging of the molecular structure via atomic-resolution STM. Accordingly, the precise characterization of this molecule via STS allows more insight into the electronic structure of adsorbed acenes with respect to their length. / Acene sind eine Klasse von polyzyklischen aromatischen Kohlenwasserstoffen mit linear kondensierten Benzolringen. Sie gelten weithin als vielversprechende Materialien für die organische und molekulare Elektronik. Jedoch sind die größeren Moleküle dieser Klasse mit mehr als fünf Ringen chemisch extrem reaktiv und zeigen eine sehr geringe Löslichkeit, daher gibt es bisher nur wenige experimentelle Untersuchungen ihrer Eigenschaften. Das Ziel dieser Arbeit ist es, Acene mit unterschiedlichen Längen auf einer metallischen Oberfläche stabilisieren und untersuchen zu können. Dabei wird der experimentelle Ansatz der Oberflächensynthese verfolgt und die jeweiligen Acene durch Reduktion von geeigneten Präkursoren direkt an einer metallischen Grenzfläche hergestellt. Hochauflösende Rastersondenmikroskopie an einzelnen Molekülen bei einer Temperatur von 5K nimmt dabei eine Schlüsselrolle im Nachweis der chemischen Umwandlung auf der Oberfläche ein. Im ersten Teil dieser Arbeit wird die Oberflächensynthese von Acenen am Beispiel von Tetracen (4-Acen) auf Cu(111) eingeführt. Die Ausgangsmoleküle mit funktionellen Gruppen adsorbieren bevorzugt mit ihrer sauerstoffreichen Seite auf dem Substrat und können dort sowohl thermisch als auch mithilfe der Spitze des Rastersondenmikroskops umgewandelt werden. In beiden Fällen wird die planare Adsorptionsgeometrie von Tetracen auf der Oberfläche mittels Rasterkraftmikroskopie mit atomarer Auflösung abgebildet. Darauf aufbauend wird Rastertunnelmikroskopie genutzt, um die Selbstassemblierung von Anthracen (3-Acen) und Tetracen nach der jeweiligen Synthese auf Au(111) zu untersuchen. Die Messungen zeigen unerwartete organische Nanostrukturen und supramolekulare Netzwerke, welche sich an der metallischen Grenzfläche durch die induzierte Oberflächenreduktion bilden können. Der zweite Teil dieser Arbeit beschäftigt sich mit den elektronischen Eigenschaften von adsorbierten Acenen. Durch die neuartige Methode der Oberflächenreduktion können einzelne Hexacene (6-Acen) auf Au(111) untersucht werden. Messungen basierend auf Rastertunnelspektroskopie geben Hinweise auf die schwache Wechselwirkung mit dem Substrat und zeigen fünf molekulare Eigenzustände, die im Experiment zugänglich sind. Die entsprechenden Abbildungen der differentiellen Leitfähigkeiten mit hoher Ortsauflösung sind in guter Übereinstimmung mit einer quantenmechanischen Modellierung. Schließlich wird die Stabilisierung von Heptacen (7-Acen) von Br-substituierten Präkursoren mittels Rastertunnelmikroskopie mit atomarer Auflösung gezeigt. Dadurch kann die elektronische Struktur von adsorbierten Acenen anhand ihrer Länge verglichen werden.

In this work we study the interesting physics of the rare earths, and the microscopic state after ultrafast magnetization dynamics in iron. Moreover, this work covers the development, examination and application of several methods used in solid state physics. The first and the last part are related to strongly correlated electrons. The second part is related to the field of ultrafast magnetization dynamics. In the first part we apply density functional theory plus dynamical mean field theory within the Hubbard I approximation to describe the interesting physics of the rare-earth metals. These elements are characterized by the localized nature of the 4f electrons and the itinerant character of the other valence electrons. We calculate a wide range of properties of the rare-earth metals and find a good correspondence with experimental data. We argue that this theory can be the basis of future investigations addressing rare-earth based materials in general. In the second part of this thesis we develop a model, based on statistical arguments, to predict the microscopic state after ultrafast magnetization dynamics in iron. We predict that the microscopic state after ultrafast demagnetization is qualitatively different from the state after ultrafast increase of magnetization. This prediction is supported by previously published spectra obtained in magneto-optical experiments. Our model makes it possible to compare the measured data to results that are calculated from microscopic properties. We also investigate the relation between the magnetic asymmetry and the magnetization. In the last part of this work we examine several methods of analytic continuation that are used in many-body physics to obtain physical quantities on real energies from either imaginary time or Matsubara frequency data. In particular, we improve the Padé approximant method of analytic continuation. We compare the reliability and performance of this and other methods for both one and two-particle Green's functions. We also investigate the advantages of implementing a method of analytic continuation based on stochastic sampling on a graphics processing unit (GPU).

Acenes are a class of polycyclic aromatic hydrocarbons (PAH) with linearly fused benzene rings. They are widely considered as promising materials for organic and molecular electronics. However, larger molecules of this class possessing more than five rings are chemically extremely reactive and show a very low solubility. Hence, large acenes are difficult to handle, and the experimental data available to date is limited. The aim of this work is to show a very promising protocol of how acenes with different lengths can be stabilized and investigated on metallic surfaces. The experimental approach of on-surface synthesis is explored to generate the respective acenes directly on the metallic substrate via the reduction of suitable precursor molecules. High-resolution scanning probe microscopy (SPM) is employed at a temperature of 5 K to verify the chemical conversion at a single-molecule level. In the first part of this work, the on-surface synthesis of acenes is introduced via the example of tetracene (4-acene) formation on Cu(111). Precursors with 1,4-epoxy moieties preferably adsorb with their oxygen-rich site facing the substrate. Subsequently, they can be deoxygenated via annealing of the substrate or by single-molecule manipulation with the tip of the scanning probe microscope. In both cases, atomic force microscopy (AFM) measurements resolve the planar adsorption geometry of tetracene on the surface with atomic resolution. Based on these findings, scanning tunneling microscopy (STM) is employed to investigate the self-assembly patterns of on-surface generated anthracene (3-acene) and tetracene molecules after synthesis on Au(111). These measurements show intriguing organic nanostructures and supramolecular networks that can form at the metallic interface upon thermally-induced surface reactions. The second part of this thesis focuses on the electronic structure of acenes adsorbed on a metallic substrate. By applying the novel method of on-surface reduction, single and isolated hexacene (6-acene) molecules are investigated on Au(111). Scanning tunneling spectroscopy (STS) measurements indicate a weak interaction with the substrate and reveal five accessible molecular resonances at the organic-metal interface. The differential conductance maps with high spatial resolution at the respective resonant bias values compare well to elastic scattering quantum chemistry-based calculations. Finally, the experimental investigations of Br-substituted precursors show the stabilization of genuine unsubstituted heptacene (7-acene), as confirmed by imaging of the molecular structure via atomic-resolution STM. Accordingly, the precise characterization of this molecule via STS allows more insight into the electronic structure of adsorbed acenes with respect to their length. / Acene sind eine Klasse von polyzyklischen aromatischen Kohlenwasserstoffen mit linear kondensierten Benzolringen. Sie gelten weithin als vielversprechende Materialien für die organische und molekulare Elektronik. Jedoch sind die größeren Moleküle dieser Klasse mit mehr als fünf Ringen chemisch extrem reaktiv und zeigen eine sehr geringe Löslichkeit, daher gibt es bisher nur wenige experimentelle Untersuchungen ihrer Eigenschaften. Das Ziel dieser Arbeit ist es, Acene mit unterschiedlichen Längen auf einer metallischen Oberfläche stabilisieren und untersuchen zu können. Dabei wird der experimentelle Ansatz der Oberflächensynthese verfolgt und die jeweiligen Acene durch Reduktion von geeigneten Präkursoren direkt an einer metallischen Grenzfläche hergestellt. Hochauflösende Rastersondenmikroskopie an einzelnen Molekülen bei einer Temperatur von 5K nimmt dabei eine Schlüsselrolle im Nachweis der chemischen Umwandlung auf der Oberfläche ein. Im ersten Teil dieser Arbeit wird die Oberflächensynthese von Acenen am Beispiel von Tetracen (4-Acen) auf Cu(111) eingeführt. Die Ausgangsmoleküle mit funktionellen Gruppen adsorbieren bevorzugt mit ihrer sauerstoffreichen Seite auf dem Substrat und können dort sowohl thermisch als auch mithilfe der Spitze des Rastersondenmikroskops umgewandelt werden. In beiden Fällen wird die planare Adsorptionsgeometrie von Tetracen auf der Oberfläche mittels Rasterkraftmikroskopie mit atomarer Auflösung abgebildet. Darauf aufbauend wird Rastertunnelmikroskopie genutzt, um die Selbstassemblierung von Anthracen (3-Acen) und Tetracen nach der jeweiligen Synthese auf Au(111) zu untersuchen. Die Messungen zeigen unerwartete organische Nanostrukturen und supramolekulare Netzwerke, welche sich an der metallischen Grenzfläche durch die induzierte Oberflächenreduktion bilden können. Der zweite Teil dieser Arbeit beschäftigt sich mit den elektronischen Eigenschaften von adsorbierten Acenen. Durch die neuartige Methode der Oberflächenreduktion können einzelne Hexacene (6-Acen) auf Au(111) untersucht werden. Messungen basierend auf Rastertunnelspektroskopie geben Hinweise auf die schwache Wechselwirkung mit dem Substrat und zeigen fünf molekulare Eigenzustände, die im Experiment zugänglich sind. Die entsprechenden Abbildungen der differentiellen Leitfähigkeiten mit hoher Ortsauflösung sind in guter Übereinstimmung mit einer quantenmechanischen Modellierung. Schließlich wird die Stabilisierung von Heptacen (7-Acen) von Br-substituierten Präkursoren mittels Rastertunnelmikroskopie mit atomarer Auflösung gezeigt. Dadurch kann die elektronische Struktur von adsorbierten Acenen anhand ihrer Länge verglichen werden.

The synthesis and properties of metal phosphonates prepared using piperazine-based bisphosphonic acids have been investigated. The ligands N,N’-piperazinebis(methylenephosphonic acid) (H₄L), and the 2-methyl (H₄L-Me) and 2,5-dimethyl (H₄L 2,5-diMe) derivatives have been prepared using a modified Mannich reaction. Hydrothermal reaction of gels prepared from metal (II) acetates and the bisphosphonic acids results in the synthesis of four structures: STA-12, Ni VSB-5, Co H₂L.H₂O and Mg H₂L. STA-12, synthesised by reaction of Mn, Fe, Co or Ni acetate with H₄L or H₄L-Me, has been investigated further. STA-12 crystallises in the space group R⁻₃, and Ni STA-12 is the most crystalline version. Its structure was solved from synchrotron data (a = b = 27.8342(1) Å, c = 6.2421(3) Å, α = β = 90°, γ = 120°), and it has large 10 Å hexagonal shaped pores. Helical chains of Ni octahedra are coordinated by the ligands, resulting in phosphonate tetrahedra pointing towards the pore space. Water is present, both coordinated to the Ni²⁺ cations and physically adsorbed in the pores. Mixed metal structures based on Ni STA-12, where some Ni is replaced in the gel by another divalent metal (Mg, Mn, Fe or Co) can also be synthesised. Dehydration of STA-12 results in two types of behaviour, depending on the metal present. Rhombohedral symmetry is retained on dehydration of Mn and Fe STA-12, the a cell parameter decreasing compared to the as-prepared structures by 2.42 Å and 1.64 Å respectively. Structure solution of dehydrated Mn STA-12 indicates changes in the torsion angles of the piperazine ring bring the inorganic chains closer together. Fe and Mn STA-12 do not adsorb N₂, which is thought to be due to the formation of an amorphous surface layer. Dehydration of Ni and Co STA-12 causes crystallographic distortion. Three phases were isolated for Ni STA-12: removal of physically adsorbed water results in retention of rhombohedral symmetry, while dehydration at 323 K removes some coordinated water forming a triclinic structure. A fully dehydrated structure (dehydrated at 423 K) was solved from synchrotron data (a = 6.03475(5) Å, b = 14.9156(2) Å, c = 16.1572(7) Å, α = 112.5721(7)°, β = 95.7025(11)°, γ = 96.4950(11)°). The dehydration mechanism, followed by UV-vis and Infra-red spectroscopy, involves removal of water from the Ni²⁺ cations and full coordination of two out of three of the phosphonate tetrahedra forming three crystallographically distinct Ni and P atoms. No structural distortion takes place on dehydration of Ni and Co STA-12 prepared using the methylated bisphosphonate, and the solids give a higher N₂ uptake as a result. Dehydrated Ni and Co STA-12 were tested for adsorption performance for fuel related gases and probe molecules. Investigations were undertaken at low temperature with H₂, CO and CO₂, and ambient temperature with CO₂, CH₄, CH₃CN, CH₃OH and large hydrocarbons. Due to the presence of lower crystallinity, Co STA-12 has an inferior adsorption performance to Ni STA-12, although it has similar adsorption enthalpies for CO₂ at ambient temperature (-30 to -35 kJ mol⁻¹). Ni STA-12 adsorbs similar amounts of CO₂ and N₂ at low temperature, indicating the adsorption mechanisms are similar. Also, it adsorbs 10 × more CO₂ than CH₄ at low pressure, meaning it could be used for separation applications. Ni STA-12 adsorbs 2 mmol g⁻¹ H₂ with an enthalpy of -7.5 kJ mol⁻¹, the uptake being due to adsorption on only one-third of the Ni²⁺ cations. The uptake for CO is 6 mmol g⁻¹, with adsorption enthalpies ranging from -24 to -14 kJ mol⁻¹. This uptake is due to adsorption on all the Ni²⁺, meaning the adsorption enthalpies are high enough to allow the structure to relax. This is also observed for adsorption of CH₃CN and CH₃OH, where there is a return to rhombohedral symmetry after uptake. The adsorption sites in dehydrated Ni and Co STA-12 were investigated via Infra-red spectroscopic analysis of adsorbed probe molecules (H₂, CO, CO₂, CH₃CN and CH₃OH). The results indicate the adsorption sites at both low and ambient temperature are the metal cations and the P=O groups. The metal cation sites are also characterised as Lewis acids with reasonable strength. STA-12 was shown to have acidic activity for the liquid phase selective oxidations of 1-hexene and cyclohexene, although there is evidence active sites are coordinated by products and/or solvents during the reaction. STA-12 also demonstrates basic activity for the Knoevenagel condensation of ethyl cyanoacetate and benzaldehyde. Modification of STA-12 by adsorption of diamine molecules causes a slight increase in the basicity, and the highest conversions are where water and diamine molecules are both present.

In this thesis, several development steps for the incremental method are presented. At first, the extension of the incremental scheme to other quantities than the energy is advanced in terms of molecular dipole moments. In this context, a revised error correction as well as the template localization for the treatment of aromatic systems are introduced. As a second enhancement, a new implementation of the template localization ensures a higher stability of this algorithm step and, thus, of the incremental scheme. Finally, pair natural orbitals (PNOs) are utilized in the incremental method with the aim of an increased efficiency. The PNO approach is re-assessed in context of the incremental expansion leading to both small incremental and PNO local errors for reaction, intermolecular interaction and cluster binding energies. The higher efficiency due to the twofold reduction of the computational efforts by the PNO and the incremental approaches is demonstrated for molecular clusters. Additionally, the complete basis set (CBS) limit is targetted by using the efficient MP2-based focal-point approach to the incremental scheme (with and without PNOs). Finally, based on these improvements of the performance, the PNO-based incremental scheme is applied to support a computational study regarding the modelling of the reaction mechanism for the base-catalyzed twin polymerization.

Les tétrazoles ont une place importante dans la chimie médicinale contemporaine par leurs caractéristiques spatiales et électroniques uniques. Leur haute teneur en azote leur confère également des qualités requises dans le développement de substances explosives et de haute énergie. Le développement de nouveaux outils synthétiques pour les créer prend donc ici tout son sens. Dans cet ouvrage, il est tout d’abord question d’une nouvelle méthode de synthèse qui génère des tétrazoles bicycliques en conditions douces par l’entremise d’azidonitriles aliphatiques séparés par trois ou quatre atomes de carbone (effet de proximité) et d’acides de Lewis. De plus, cette méthode de synthèse présente une réaction tandem qui génère des tétrazoles oxabicycliques 1,5-dialkylés via une cycloaddition 1,3-dipolaire diastéréosélective à partir d’azidoacétals ou d’azidocétals arborant un azoture proximal. La réaction s’effectue dans le nitrométhane de 0 °C à la température ambiante avec du TMSCN et est promue par une variété d’acides de Lewis dont le BF3OEt2. Les aspects mécanistiques de la réaction (l’ouverture des acétals, l’équilibre entre les éthers de cyanhydrine, la cycloaddition 1,3-dipolaire diastéréosélective et le réarrangement de Boyer-Schmidt-Aubé) ainsi que les paramètres réactionnels (solvants, acides de Lewis, stœchiométrie, sources de cyanure, etc.) seront en outre abordés. Ensuite, le motif de tétrazole oxabicyclique a été l’objet de diversifications, de fonctionnalisations et de transformations afin d’en valoriser l’utilité. Des réactions d’alkylations, d’azoturations radicalaires, de bêta-éliminations et de diversifications de la chaîne latérale ont été étudiées. De ces mêmes motifs de tétrazoles, la synthèse de tétrazoles azabicycliques et celle de morpholines 2,6-polysubstituées ont aussi été investiguées. La synthèse d’un sel de tétrazolium et l’alkylation de 5-tétrazolyllithiums ont aussi fait l’objet d’études préliminaires. Enfin, une étude théorique en DFT a été effectuée pour mieux comprendre l’équilibre tétrazole-azidoazométhine sur des motifs de types benzo- et pyrido- diazidodiazines parents à la 6-azidotétrazolo[5,1-a]phthalazine, un métabolite toxique du Gymnodinium breve (Ptychodiscus brevis, aussi actuellement connu sous le nom de Karenia brevis). Les aspects thermodynamiques, les états de transition, les orbitales HOMO, les cartes de potentiels d’ionisation locaux, les cartes de densité de la LUMO, les effets de solvant et certains paramètres permettant d’évaluer l’aromaticité (indices de Bird, ordres de liaison minimaux de Jug, indices HOMA et NICS) ont été considérés dans l’étude. Le constat a été que certaines des analyses théoriques peuvent constituer de bons outils prédictifs, particulièrement avec des considérations thermodynamiques, mais que cette approche a aussi ses limites qui sont principalement dues aux incertitudes inhérentes aux calculs théoriques. / Tetrazoles have an important place in contemporary medicinal chemistry due to their unique spatial and electronic characteristics. Their high nitrogen content also gives them the qualities required for the development of explosive and high energy substances. The development of new synthetic tools to create them takes here all its meaning. Therefore, in this work, a new synthesis method that generates bicyclic tetrazoles under mild conditions using aliphatic azidonitriles separated by three or four carbon atoms (proximity effect) and Lewis acids will first be discussed. In addition, a tandem reaction which generates 1,5-dialkylated oxabicyclic tetrazoles via a diastereoselective 1,3-dipolar cycloaddition from azidoacetals or azidoketals bearing a proximal azide will also be disclosed. The reaction is carried out in nitromethane at 0 °C to room temperature with TMSCN and is promoted by a variety of Lewis acids including BF3OEt2. The mechanistic aspects of the reaction (acetal opening, equilibrium between cyanohydrin ethers, diastereoselective 1,3-dipolar cycloaddition and Boyer-Schmidt-Aubé rearrangement) as well as the reaction parameters (solvents, Lewis acids, stoichiometry, cyanide sources, etc.) will be discussed. Furthermore, the oxabicyclic tetrazole unit was involved in diversifications, functionalizations and transformations to enhance its utility. Reactions of alkylations, radical azidations, beta-eliminations and diversifications of the side chain were applied. From these same tetrazole units, the synthesis of azabicyclic tetrazoles and that of 2,6-polysubstituted morpholines was also investigated. The synthesis of a tetrazolium salt and the alkylation of 5 tetrazolyllithiums were also the subject of preliminary studies. Finally, a theoretical DFT study was carried out to have a better understanding of the tetrazole-azidoazomethine equilibrium on benzo- and pyrido- diazidodiazines similar to 6 azidotetrazolo [5,1-a] phthalazine, a toxic metabolite from Gymnodinium breve (Ptychodiscus brevis, actually known as Karenia brevis). Thermodynamic aspects, transition states, HOMO orbitals, local ionization potential maps, LUMO density maps, solvent effects, and some parameters to evaluate the aromaticity (Bird index, Jug minimum bond order, HOMA index and NICS) were considered in the study. It has been noted that some of the theoretical analysis can be good predictive tools, particularly with thermodynamic considerations, but they also have their limits, which are mainly due to the uncertainties inherent in the theoretical calculations.