The X-ray absorption spectrum of silicon in of SiCl4 has been calculated for the LIII and LII edges. The resulting spectrum has been vibrationally resolved by considering the symmetric stretch vibrational mode and the results has been compared to experiment [4]. One peak from the experiment was found to be missing in the calculated vibrationally resolved spectrum. The other calculated peaks could be matched to the corresponding experimental peaks although significant basis set effects are present. An investigation of one peak beyond the Franck–Condon principle shows it to be a good approximation in the case of the studied system.

The work presented in this thesis concerns the dynamics in π-conjugated hydrocarbon systems. Due to the molecular bonding structure of these systems there exists a coupling between the electronic system and the phonons of the lattice. If this interaction, which is referred to as the electron-phonon (e-ph) coupling, is sufficiently strong it may cause externally introduced charge carriers to self-localize in a polarization cloud of lattice distortions. These quasi-particles are, if singly charged, termed polarons, the localization length of which, aside from the e-ph coupling strength, also depend upon the structural and energetic disorder of the system. In disordered systems localization is strong and transport is facilitated by nonadiabatic hopping of charge carriers from one localized state to the next, whereas in well-ordered systems, where extended states are formed, adiabatic transport models apply.Despite great academic efforts a unified model for charge transport in π-conjugated systems is still lacking and further investigations are necessary to uncover the basic physics at hand in these systems. The call for such efforts has been the main guidelines for the work presented in this thesis and are related to the topics of papers I-IV. In order to capture the coupled electron-lattice dynamics, we use a methodological approach where we obtain the time-dependence of the electronic degrees of freedom from the solutions to the time-dependent Schrödinger equation and determine the ionic motion in the evolving charge density distribution by simultaneously solving the lattice equation of motion within the potential field of the ions. The Hamiltonian used to describe the system is derived from an extension of the famous Su-Schrieffer-Heeger (SSH) model extended to three-dimensional systems.In papers I-III we explore the impact of phenylene ring torsion on delocalization and transport properties in poly(para-phenylene vinylene) (PPV). The physics that we are particularly interested in relates to the reduced electron transfer integral strength across the interconnection between the phenylene rings and the vinylene groups upon ring torsion. Keeping this in mind, we demonstrate in paper I the impact of static ring torsion on intrachain mobility and provide a detailed analysis of the influence of the potential barriers (due to consecutive ring torsion) on the nature of charge carrier propagation. In paper II we extend our initial approach to include also the dynamics of ring torsion. We show that without any externally applied electric field, this type of dynamics is the dominant property controlling intrachain propagation, but that when an external electric field is applied, charge carriers may traverse the potential barriers through a process that involves nonadiabatic effects and a temporary delocalization of the polaron state. Finally, in paper III we study the impact of the lattice dynamics on the electron localization properties in PPV and show that the phenylene ring torsion modes couples strongly to the electronic wave function which gives rise to electron localization at room temperature.In papers IV and V we focus on the dynamics of molecular crystals using a stack of pentacene molecules in the single crystal configuration as a model system, but study, in paper IV, the transport as a function of the intermolecular interaction strength, J. We observe a smooth transition from a nonadiabatic to an adiabatic polaron drift process over the regime 20<J<120 meV. For intermolecular interaction strengths above J≈120 meV the polaron is no longer stable and transport becomes band-like. In paper V, finally, we study the internal conversion processes in these systems, which is the dominant relaxation channel from higher lying states. This process involves the transfer of energy from the electronic system to the lattice. Our results show that this process is strongly nonadiabatic and that the relaxation time associated with large energy excitations is limited by transitions made between states of different bands. / I dagens samhälle är elektroniken ett allt viktigare och större inslag i vår vardag. Vi ser på TV, talar i mobiltelefoner, och arbetar på datorer. I hjärtat av denna teknologi finner vi diskreta komponenter och integrerade kretsar utformade främst för att styra strömmen av elektroner genom halvledande material. Traditionellt sett har kisel eller olika former av legeringar använts som det aktiva materialet i dessa komponenter och kretsar, men under de senaste 20 åren har såväl transistorer som solceller och lysdioder realiserats där det aktiva materialet är organiskt, d.v.s., kolbaserat.Vi befinner oss för tillfället mitt uppe i det kommersiella genombrottet för organisk elektronik. Redan idag säljs många MP3-spelare och mobiltelefoner med små skärmar där varje pixelelementen utgörs av organiska ljusemitterande dioder (OLEDs), men teknologin håller redan på att introduceras i mer storskaliga produkter som datorskärmar och TV-apparater som därigenom skulle kunna göras energieffektivare, tunnare, flexiblare och på sikt också billigare. Andra tekniska tillämpningsområden för organisk elektronik som förutspås en lysande framtid är RFID-märkning, organiska solceller, och elektronik tryckt på papper, men även smarta textiler och bioelektronik har stor utvecklingspotential.Den kanske största utmaningen kvarstår dock, att skapa elektroniska kretsar och komponenter uppbyggda kring enskilda molekyler, s.k. molekylär elektronik. Mycket snart närmar vi oss den fysikaliska gränsen för hur små komponenter som vi kan realisera med traditionella icke-organiska material som kisel och en stor drivkraft bakom forskningen på halvledande organiska material har varit just visionen om molekylär elektronik som inte är mer än några miljondelars milimeter stora. För detta ändamål krävs en mycket nogrann kontroll av tillverkningsprocesserna liksom en detaljförståelse för hur molekylerna leder ström och hur denna förmåga kan manipuleras för att realisera såväl traditionella som nya komponenter.I denna avhandling presenteras en översikt av den fysik som möjliggör ledningsförmåga hos särskilda klasser av organiska material, s.k. π-konjugerade system, samt de forskningsresultat som utgör mitt bidrag till denna disciplin. En av utmaningarna på området är den komplexitet som de organiska materialen erbjuder: laddningsprocesserna påverkas nämligen av en rad olika faktorer såsom laddningstäthet, temperatur, pålagd spänning, samt molekylernas former och inbördes struktur. I detta arbete har jag utifrån en vidareutveckling av existerande modeller genom numeriska datasimuleringar undersökt effekten av de senare tre faktorerna på elektronstrukturen, laddnigstransporten och energidissipation i denna klass av material. / Center of Organic Electronics (COE)

Time-dependent molecular properties are important for the experimental characterization of molecular materials. We show how these properties can be calculated, for optical and x-ray frequencies, using novel quantum chemical methods. For xray absorption there are important relativistic effects appearing, due to the high velocity electrons near the atomic nuclei. These effects are treated rigorously within the four-component static exchange approximation. We also show how electron correlation can be taken into account in the calculation of x-ray absorption spectra, in time-dependent density functional theory based on the complex polarization propagator approach. The methods developed have been applied to systems of experimental interest|molecules in the gas phase and adsorbed on metal surfaces. The effects of molecular vibrations have been take into account both within and beyond the harmonic approximation.

This thesis deals with theoretical studies of the electronic structure of molecules used in the context of molecular electronics. Both studies with model Hamiltonians and first principle calculations have been performed. The materials studied include molecular crystals of pentacene and DNA, which are used as active material in field-effect transistors and as tentative molecular wires, respectively. The molecular magnet compound TCNE and surface modification by means of chemisorption of TDAE on gold are also studied. Molecular crystals of pentacene are reported to have the highest field-effect mobility values for organic thin film field-effect transistors. The conduction process in field-effect transistors applications occurs in a single layer of the molecular crystal. Hence, in studies of transport properties molecular crystals of pentacene can be considered as a two dimensional system. An open question of these system is if the charge transport is bandlike or if as a result of disorder is a hopping process. We address this question in two of the included papers, paper I and paper II. The conducting properties of DNA are of interest for a broad scientific community. Biologist for understanding of oxidatively damaged DNA and physicist and the electronics community for use as a molecular wire. Some reports on the subject classifies DNA as a conductor while other report insulating behavior. The outcome of the investigations are heavily dependent on the type of DNA being studied, clearly there is a big difference between the natural and more or less random sequence in, e.g., λ-DNA and the highly ordered syntethic poly(G)-poly(C) DNA. It has been suggested that long-range correlation would yield delocalized states, i.e., bandlike transport, in natural DNA, especially in the human chromosome 22. In paper III we show that this is not the case. In general our results show that DNA containing an approximately equal amount of the four basis is an insulator in a static picture. An emerging research field is spintronics. In spintronic devices the spin of the charge carrier is as important as the charge. One can envision a device where spin alone is the carrier of information. In realizing spintronic devices, materials that are both magnetic and semiconducting are needed. Systems that exhibit both these properties are organic-based magnets. In paper IV the electronic structure of the molecular magnet compound TCNE is studied, both experimentally and theoretically. The injection of carriers from metal contacts to organic semiconductors is central to the performance of organic based devices. The interface between the metal contact and the organic material has been pointed out to be one of the device parameters that most significantly influences the device performance. This relates to the process of injection of charge carriers in to the organic material. In some contact and organic material combinations the energy barrier for charge injection can be very high. The barrier can be reduced by modify the interface dipole, this is achieved by a monolayer of adsorbed molecules at the interface. The molecule TDAE chemisorbed on gold is studied in paper V.

Density functional theory has been used to investigate cathode materials for rechargeable batteries, carbon nanotube interactions with catalyst particles and transition metal catalyzed hydrogen release in magnesium hydride nanoclusters. An effort has been made to the understand structural and electrochemical properties of lithium iron silicate (Li2FeSiO4) and its manganese-doped analogue. Starting from the X-ray measurements, the crystal structure of Li2FeSiO4 was refined, and several metastable phases of partially delithiated Li2FeSiO4 were identified. There are signs that manganese doping leads to structural instability and that lithium extraction beyond 50% capacity only occurs at impractically high potentials in the new material. The chemical interaction energies of single-walled carbon nanotubes and nanoclusters were calculated. It is found that the interaction needs to be strong enough to compete with the energy gained by detaching the nanotubes and forming closed ends with carbon caps. This represents a new criterion for determining catalyst metal suitability. The stability of isolated carbon nanotube fragments were also studied, and it is argued that chirality selection during growth is best achieved by exploiting the much wider energy span of open-ended carbon nanotube fragments. Magnesium hydride nanoclusters were doped with transition metals Ti, V, Fe, and Ni. The resulting changes in hydrogen desorption energies from the surface were calculated, and the associated changes in the cluster structures reveal that the transition metals not only lower the desorption energy of hydrogen, but also seem to work as proposed in the gateway hypothesis of transition metal catalysis.

The absorption properties of the Pt1 chromophore at room temperature have been studied. Stretch, bend and torsion parameters for Pt(II), P, C (type 1, 2 and 4) and H have been parameterized for use in the MM3 force field. Parameters were fitted to energies computed at the B3LYP level of theory. The parameterized model was used to perform molecular dynamics simulations at room temperature. This was done for several environments and for time periods of up to 200 ps. Absorption properties were computed for snapshots from the dynamics, from which average absorption spectra were created. A conformational broadening of around 40 nm was found in the theoretical spectra, which is in good agreement with experiments. Due to a lack of solvent-solute interactions and the use of a less extensive basis set, a systematic blue shift of 40 nm is evident in the computed spectra.

The main purpose of this thesis is to implement the Gauss--Legendre quadrature for the dispersion coefficient. This has been done and can be now be made with different number of points. The calculations with this implementation has shown that the relativistic impact on helium, neon, argon and krypton is largest for krypton, that has the highest charge of its nucleus. It was also seen that the polarizability of neon as a function of the imaginary angular frequency decreases monotonically from a static value.

A novel method by which to calculate the near edge X-rayabsorption fine structure region of the X-ray absorption spectrum has been derived and implemented. By means of damped coupled cluster theory at coupled cluster levels CCS, CC2, CCSD and CCSDR(3), the spectra of neon and methane have been investigated. Using methods incorprating double excitations, the important relaxation effects maybe taken into account by simultaneous excitation of the core electron and relaxation of other electrons. An asymmetric Lanczos-chain driven approach has been utilized as a means to partially resolve the excitation space given by the coupled cluster Jacobian. The K-edge of the systems have been considered, and relativistic effects are estimated with use of the Douglas--Kroll scalar relativistic Hamiltonian. Comparisons have been made to results obtained with the four-component static-exchange approach and ionization potentials obtained by the {Delta}SCF-method. The appropriate basis sets by which to describe the core and excited states have been been determined.  The addition of core-polarizing functions and diffuse or Rydberg functions is important for this description. Scalar relativistic effects accounts for an increase in excitation energies due to the contraction of the 1s-orbital, and this increase is seen to be 0.88 eV for neon. The coupled cluster hierachy shows a trend of convergence towards the experimental spectrum, with an 1s -> 3p excitation energy for neon of an accuracy of 0.40 eV at a relativistic CCSDR(3) level of theory. Results obtained at the damped coupled cluster and STEX levels of theory, respectively, are seen to be in agreement, with a mere relative energy shift.

The goal of this thesis is to develop a constraint based viscoplastic fluid model suitable for time-efficient dynamics simulation in 3D of granular matter. The model should be applicable to both the static and dense flow regime and at large pressures. The thesis is performed for UMIT Research Lab at Umeå University. It is a part of the research at UMIT connected to LKAB and Volvo CE and its applications can be in simulating industrial processes or training simulators. My work is based on previous work done by Claude Lacoursière, Martin Servin and Kenneth Bodin. They have created a constraint fluid model based on {\sph} and Claude's PhD. thesis. This model is extended with additional constraints to handle shear forces, which is necessary to model granular material. Some test cases are specified and compared visually to each other and to the results of other work. The model seems to work visually but more analysis and larger systems are needed to be certain. The model should scale well and is well suited for parallellization.

<p>The X-ray absorption spectrum of silicon in of SiCl4 has been calculated for the LIII and LII edges. The resulting spectrum has been vibrationally resolved by considering the symmetric stretch vibrational mode and the results has been compared to experiment [4]. One peak from the experiment was found to be missing in the calculated vibrationally resolved spectrum. The other calculated peaks could be matched to the corresponding experimental peaks although significant basis set effects are present. An investigation of one peak beyond the Franck–Condon principle shows it to be a good approximation in the case of the studied system.</p>