In the search for a sustainable and environmentally friendly energy source, artificial photosynthesis has been proposed  as a promising solution. Using water as a substrate, solar energy can be utilised to store energy in the chemical form of hydrogen fuel. In part of this global scientific effort, this thesis work focuses on enabling molecular dynamics simulations of a particular set of ruthenium centred  water oxidation catalysts. The new catalysts show great success because of a binuclear  reaction  pathway in aqueous solution which makes it very interesting to model and investigate. Utilising quantum  mechanical tools, a set of molecular mechanics force field parameters for Ru-involved bonds, angles, torsions, and partial charges was successfully obtained and examined. The work allows future large scale simulation of water  oxidation and oxygen evolution in order to gain understanding and improve artificial photosynthesis.

The purpose of this study is to observe what modifying the surface of cellulose nanofibrils may imply for their interactions with a surrounding saline aqueous solution. This will be studied by using GROMACS, a molecular dynamic simulation software. In particular, we will analyse the modified surfaces hydrophilicity compared to native nanocellulose. This will subsequently have an impact on the nanofibrils readiness to aggregate to one another and disperse in the solution. Specifically two types of surface modifications will be studied, sulfonation and carboxy- lation. The hydrophilicity of the surfaces will be determined by analysing the density profiles of the systems wherein the modified surfaces interacts with the aqueous solutions. Also, the energies from the interactions of the simulated systems will be studied. We concluded that both modifications increases the surfaces interactions with the sur- rounding solution. Modifying the surface of the cellulose nanofibril with sulfonate will increase the surfaces attraction towards water and may provide the best rate of dispersion in aqueous solutions and best prohibit aggregation. Carboxylation of the surface provides similar hydrophilic results as the sulfonation but not as prevalent.

Thermodynamically, native cellulose nano fibrils are more stable in an aggregated state. The aggregated state is however not useful from a material development perspective. Therefore much research has been done to stabilize the dispersal of the fibrils. One method to overcome this instability is by surface substitution of the O6 hydroxyl group with carboxylate groups, to make highly charged fibrils in aqueous solutions. It is therefore of much interest to understand the interaction of highly charged fibrils in aqueous solutions. In this study, we aim to model the interaction potential energy between native and surface modified cellulose nanofibrils in order to understand under what conditions the contribution from the dipole interactions can be neglected. To achieve this we propose to use a continuum electrostatic approach, modeling the electrostatic interactions as a function of the fibrils relative dipole orientation, separation, surface charge as well as ionic strength of the solution, by means of using the Poisson-Boltzmann equation.

Här undersöks en strategi som behandlar dendrittillväxt på en solid litiumanod i ett litiumbatteri. Med hjälp av täthetfunktionalsteori adsorberades fyra flytande kristaller på litiumytan vilket ledde till en gränsskiktsstabilisering. Denna stabilisering har i en tidigare rapport länkats till dendrittillväxt i en fasfältsmodell. Fasfältsmodellen replikerades ej i denna rapport utan det ses som ett eventuellt nästa steg. Molekylerna interagerade starkt med ytan och de beräknade adsorptionsenergierna hade stor inverkan på litiumytans gränsskiktsenergi. De flytande kristallernas fas simulerades också, vilken hade en beräknad kohesivenergi i samma storleksordning som flytande vatten. Denna energi var lägre än adsorptionsenergierna, vilket tyder på att det finns en drivkraft för molekylerna att interagera med ytan. Vidare så undersöktes redoxstabiliteten hos molekylerna, där det visade sig att två av molekylerna hade LUMO-energier under Ferminivån hos litium. Dessa molekyler är således inte stabila nära litiumytan, utan kommer eventuellt ta del i elektrokemiska reaktioner. Slutligen så undersöktes diffusionsbarriären hos adsorberade litiumatomer. Här jämfördes barriären mellan fall då molekyler var adsorberade och inte, och det visade sig att med adsorberade molekyler så är diffusionsbarriären högre. / A strategy to suppress the growth of dendrites on solid state lithium anodes was investigated. Using density functional theory, four liquid crystal molecules were adsorbed on a solid lithium surface leading to an interfacial stabilization. This stabilization has earlier been used as a descriptor in a phase-field model which investigated dendrite suppression. The replication of this phase-field model was out of the scope of this thesis and left as future work. The LC molecules interacted strongly with the surface, and the calculated adsorption energies had an considerable impact on the interfacial energies of the lithium surface. A liquid crystal phase was also simulated, with a cohesive energy of the same magnitude as liquid water. This energy was lower than the adsorption energies, indicating that there is a driving force for the LC molcules to adsorb to the surface. Furthermore, the redox stability of the molecules in the proximity of the lithium surface was investigated, where two of them had LUMO energies below the Fermi level of lithium. Those two molecules were thus not considered sufficiently stable to not take part in any electrochemical reactions with solid lithium. Finally, the surface diffusion barrier of adsorbed lithium atoms was investigated. The barrier with and without the liquid crystals adsorbed to the surface was compared, which showed that the diffusion barrier was even higher with the molecules adsorbed.

No description available.

Everything in the universe is made up of elements from the periodic table. Each element has its own role that it plays in the formation of things it makes up. For instance, pencil lead is graphite. A series of honeycomb-like structures made up of carbon stacked on top of one another. Carbon’s neighbor to the left, boron doesn’t like to form such stacked honeycomb-like structures. But, what if there was a way to make boron act like carbon so it did like to form such structures? That question is the basis of the electronic transmutation concept presented in this dissertation. Electronic transmutation states that an element, such as boron, can behave structurally like carbon (form stacked honeycomb structures) if you make them valence (outer most) isoelectronic (“iso”- same; “electronic”- electrons), so both would have the same number of outer most electrons. As a result, chemists would have a new tool to aid in the rational design of new materials.

Comprendre les réactions biologiques requiert l'utilisation de composés capables de transférer des électrons de manière sélective et de stabiliser des intermédiaires réactionnels. Ce travail s'est intéressé à la conception et à la réactivité de complexes de lanthanide divalents qui ont ce type de propriétés.Dans un premier temps, la réduction de deux molécules organiques, la phénanthroline et la benzophenone, a été étudiée. Les données thermodynamiques obtenues avec la phénanthroline ont permis de construire un ensemble de données de références de différentes fonctionnelles de la densité. Des méthodes de type TDDFT et CASSCF ont été ensuite mises en oeuvre afin de reproduire les spectres UV-visibles.Par la suite, les radicaux benzophenone et phénanthroline ont été utilisés afin de réaliser des réactions radicalaires. L'utilisation du radical tempo a permis de réaliser des réactions de réduction induite par les effets stériques des complexes. La compétition entre la benzophenone et la phénanthroline a également été étudiée et a permis de réaliser des couplages de type Minisci, qui sont inédits pour des complexes de lanthanides.Enfin, la réduction de composés organométalliques via un ligand N-hétérocyclique a été réalisée. Deux de ces composés ont été comparés vis à vis de la stabilisation de complexes de palladium au degré d'oxydation +IV. L'importance du ligand a été de plus étudiée grâce à des calculs CASSCF et DFT qui ont montré que certains types de ligands permettaient un transfert électronique plus direct jusqu'au palladium. / Understanding biological reactions require the use of molecules that can transfer electrons selectively and stabilise key intermediates. This work is interested into the design and the reactivity of divalent lanthanides that possess this kind of property.Firstly, organic molecules, i.e. phenanthroline and benzophenone, were reduced by samarium complexes. The thermodynamic data obtained for phenanthroline reduction was used to perform a benchmark study on different density functionals. TDDFT and CASSCF methods were then used to understand the electronic structure of the complexes and compared to the UV-visible spectrum of the molecules.Then, benzophenone ketyl and phenanthroline radicals have been used to perform radical reactions. Reactions with tempo led to already observed sterically induced reduction which mechanism was investigated. The competition between phenanthroline and benzophenone led to Minisci couplings that were never described with lanthanide complexes.Finally, the electron was transferred to organometallic species containing palladium via a bridge N-heterocycle ligand. Two of such species were compared towards the stabilisation of palladium at the IVth oxidation state. The importance of the ligand was further assessed by a combination of DFT and CASSCF calculations showing that certain ligands enabled a more direct transfer towards the palladium centre.

The aim of this study is to study the ground-state of various elements including Hydrogen molecules and Heliumatoms using a self written Density Functional Theory code. We limit ourselves to simple linear moleculesusing cylindrical symmetry, for which the computational difficulty is manageable and appropriate for anundergraduate thesis. We focus on the binding length and energy of the molecules stated here. Charge densityis calculated using the Poisson equation, which is used to calculate the potential and correlation potential. From the distance dependent of the total energy, the chemical bond length can be determined. The results showa total energy for a Hydrogen molecule is -31.3 eV and most optimal binding length is identified at 0.76 Å.

No description available.

A theoretical framework for calculating electron transport through molecular junctions is presented. It is based on scattering theory using a Green's function formalism. The model can take both elastic and inelastic scattering into account and treats chemical and physical bonds on equal footing. It is shown that it is quite reliable with respect to the choice of functional and basis set. Applications concerning both elastic and inelastic transport are presented, though the emphasis is on the inelastic transport properties. The elastic scattering application part is divided in two part. The first part demonstrates how the current magnitude is strongly related to the junction width, which provides an explanation why experimentalists get two orders of magnitude differences when performing measurements on the same type of system. The second part is devoted to a study of how hydrogenbonding affects the current-voltage (I-V) characteristics. It is shown that for a conjugated molecule with functional groups, the effects can be quite dramatic. This shows the importance of taking possible intermolecular interactions into account when evaluating and comparing experimental data. The inelastic scattering part is devoted to get accurate predictions of inelastic electron tunneling spectroscopy (IETS) experiments. The emphasis has been on elucidating the importance of various bonding conditions for the IETS. It is shown that the IETS is very sensitive to the shape of the electrodes and it can also be used to discriminate between different intramolecular conformations. Temperature dependence is nicely reproduced. The junction width is shown to be of importance and comparisons between experiment as well as other theoretical predictions are made. / QC 20101118