Att förutsäga egenskaper hos material och kemiska system är en viktig komponent för teoretisk och teknisk utveckling i fysik, kemi och biologi. Ett systems egenskaper styrs till stor del av dess elektrontillstånd. Datorprogram som baseras på täthetsfunktionalsteori kan beskriva elektronkonfigurationer mycket noggrant. Täthetsfunktionalsteorin hanterar all kvantmekanisk energi exakt, förutom ett mindre bidrag, utbytes-korrelationsenergin. Avhandlingen diskuterar existerande approximationer av utbytes-korrelationsenergin och presenterar en ny metod för konstruktion av funktionaler som hanterar detta bidrag---delsystems-funktionalmetoden. Flera teoretiska resultat relaterade till funktionalutveckling ges. En utbytes-korrelations-funktional har konstruerats helt utan empiriska antaganden (dvs, från första-princip). Funktionalen har använts för att beräkna gitterkonstant, bulkmodul och vakansenergi för aluminium, platina och kisel. Arbetet förväntas vara generellt tillämpbart inom området för täthetsfunktionalsteoriberäkningar / The prediction of properties of materials and chemical systems is a key component in theoretical and technical advances throughout physics, chemistry, and biology. The properties of a matter system are closely related to the configuration of its electrons. Computer programs based on density functional theory (DFT) can calculate the configuration of the electrons very accurately. In DFT all the electronic energy present in quantum mechanics is handled exactly, except for one minor part, the exchange-correlation (XC) energy. The thesis discusses existing approximations of the XC energy and presents a new method for designing XC functionals---the subsystem functional scheme. Numerous theoretical results related to functional development in general are presented. An XC functional is created entirely without the use of empirical data (i.e., from so called first-principles). The functional has been applied to calculations of lattice constants, bulk moduli, and vacancy formation energies of aluminum, platinum, and silicon. The work is expected to be generally applicable within the field of computational density functional theory. / QC 20100830

This thesis describes the development and characterization of a compact high-brightness liquid-metal-jet anode x-ray source. Initial calculations show that a source based on this concept could potentially lead to a >100-fold increase of the brightness compared to current state-of-the-art rotating-anode x-ray sources. This improvement is due to an increased thermal load capacity of the anode. A low-power proof-of-principle source has been built, and experiments show that the liquid-metal-jet anode can be operated at more than an order of magnitude higher power densities than modern solid-metal anodes. This brightness enhancement has been utilized to acquire in-line phase-contrast images of weakly absorbing objects with substantially shorter exposure times than previously reported. To be able to target different application areas different liquid-jet-anode materials have been tested. The Sn-jet anode could potentially be used in mammography examinations, whereas the Ga-jet could be utilized for, e.g., protein-structure determination with x-ray diffraction. Scaling to higher power and brightness levels is discussed and seems conceivable. A potential obstacle for further development of this source concept, the generation of a microscopic high-speed liquid-metal jet in vacuum, is investigated and is proven to be feasible. Dynamic-similarity experiments using water jets to simulate 30-μm, ~500-m/s tin and gallium jets show good coherence and directional stability of the jet. Other potential difficulties in the further source development, such as excessive debris emission and instabilities of the x-ray emission spot, are also investigated in some detail. / QC 20100915

Investigations and measurements of metastable states are in many ways very important. Spectroscopists, theorists and astrophysicists have all great interest and requirements regarding knowledge about such states and their properties. One of the interesting properties is the lifetime of each state and lifetime measurements are therefore of great importance. It is necessary to have a long observation time when performing investigations on metastable states in ions and there are some different methods to fulfill this requirement. One method to store ions is to use an ion storage ring in which the ions are bent in circle by a magnetic or an electrostatic field. The storage ring method combined with a laser probing technique constitutes the basis for the papers described in this thesis. The thesis also contains some theoretical background to the experiments together with explanations regarding the experimental setup, the procedure for the laser probing technique and the systematic effects that have to be considered. The thesis includes results from nine different positive and negative singly charged ions. The experimental and theoretical results are presented and compared. The experiments have been done in collaboration with E. Biémont's theoretical group in Belgium, with S. Johansson's astrophysical group in Lund and D. Hanstorp's group in Gothenburg.

This thesis describes separate studies of high-energy Rydberg and ion-pair states in small molecules using resonant multi-photon ionisation spectroscopy. * OODR/REMPI study of ungerade Rydberg states in O2 The energy region between 75000 and 99900 cm-1 of O2 has been studied using optical-optical double resonance (OODR) with resonance enhanced multi-photon ionisation (REMPI). Three-photon excitation via single rotational levels of the b(1Σ+g ) valence state was used to study np (n=3–10) and nf (n=4–9) Rydberg states converging on O2+X(2Π1/2,g) and X(2Π3/2,g). The excitation pathway picks out non-predissociated states that are singlet in the (Λ,S) coupling scheme – suitable for np states for n ≥8, or are linear combinations of equal weight of singlet and triplet-spin states in the (Ω,ω) coupling scheme which was found to be suitable for nf states for all values of n. * OTR/RI study of Rydberg and ion-pair states in I2 Optical triple resonance (OTR) together with resonance ionisation (RI) has been used to study the ungerade manifold of molecular iodine between 57000 and 73000 cm-1 via the E 0g+(3P2) ion-pair state. Two 6s Rydberg states with 0 +u symmetry based on excited states of the ion core have been observed. During this study we also observed electric-field-induced mixing of nearly isoenergetic rovibrational levels of the E0gP+(3P2) and D0u+(3P2) ion-pair states. Detectable mixing with an applied field of 1kV/cm occurs over a range of energy level separations of ≤0.3 cm-1. * (2+1)and (3+1) REMPI study of pyrrole (C4H5N) The two- and three-photon REMPI spectra of Rydberg states of pyrrole (C4H5N) have been recorded using circularly and linearly polarised light. The spectra were compared to the single-photon absorption spectrum of pyrrole and a similar study of furan (C4H4O). Although the ionisation spectra of pyrrole were considerably weaker than corresponding furan spectra, a strong propensity for excitation of d series with two photons and p and f series with three photons was observed for both molecules. The totally symmetric nd-Rydberg series associated with the first ionisation energy, [A2]nd;A1, was identified from n=3 to n=15 and extrapolated to obtain IE1. / QC 20101006

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A series of studies of f-electron systems based on density functional theory methods have been performed.  The focus of the studies has been on magnetic and structural properties, as well as investigating ways to handle strong electron correlation in these systems. A version of the self-interaction correction (SIC) method has been developed for a full-potential linear muffin-tin orbital method. The method is demonstrated to have the strong capabilities of previous SIC implementations, to study energetics and phase stabilities of d- and f-electron systems with localisation-delocalisation transitions, but with no geometrical constraints from the underlying band structure method. The method is applied to the high-TC superconductor CeOFeAs, in which the f-shell of the Ce atoms is argued to undergo a Mott transition to a delocalised state under pressure. The non-collinear magnetic structures of two rare earth compounds, TbNi5 and CeRhIn5 have been studied, and in both cases the complex magnetic ordering can be attributed to the effects of Fermi surface nesting. The magnetic properties of the FeMnP0.75Si0.25 system has been studied and found to have an extreme sensitivity to the amount of disorder of the Fe-Mn sublattice. Elements with valence f electrons typically exhibit very complex phase diagrams, with the frequently occurring phenomenon that they melt from a bcc phase that is unstable in calculations based solely on the electronic structure. The high temperature bcc phase of the elements La and Th were studied by means of the self-consistent ab initio lattice dynamics method that accounts for phonon-phonon interaction. Delicate magnetic and structural properties are often sensible to details of how the Brillouin zone (BZ) integration is performed. An improved scheme is proposed that adapts to the BZ mesh and allows for better energy convergence of small energy differences in the smearing type methods. Correlation effects in the 5f-states of plutonium has in recent years been the focus of attention for many theoretical studies employing extensions to DFT schemes. These different schemes have often produced large variations in 5f occupation numbers, and therefore a survey was made of experimental occupation numbers and 4f core level shifts to establish a value for the 5f occupation without any computational bias.

This thesis deals with fragmentation of complex molecular ions, especially biomolecules, in gas phase collision experiments. The aim is to investigate the relations between energy deposition and fragmentation and to shed light on the mechanisms behind energy and charge transfer processes in collisions involving the building blocks of life. Further, the question how a solvent environment influences the dissociation behavior is elucidated. In the first part of the thesis, results from different collision experiments with biomolecular ions are presented, focusing on electron capture induced dissociation of hydrated nucleotides and small peptides. The investigated processes may be relevant for the understanding of radiation damage and the optimization of sequencing methods used in protein research. Our results clearly demonstrate that effects due to surrounding solvent molecules are substantial. While the dissipation of internal energy by evaporation of the loosely bound solvent molecules may protect the biomolecule, the influence which this environment has on the electronic structure may lead to an enhancement or suppression of certain dissociation channels. The second part of the thesis focuses on recent instrumental developments. Here, the aim was to optimize and complement the techniques used in the experiments above and to have versatile tools available for different kinds of gas phase collision studies involving complex molecular ions. Therefore, we have constructed an electrospray ion source platform for the preparation of intense beams, with options of accumulation and cooling of mass selected ions, allowing for a large variety of experiments. This device is also intended to serve as an ion source for the new storage ring facility DESIREE (DoubleElectroStatic Ion Ring ExpEriment), which is currently under construction at Stockholm University. In these unique storage rings, oppositely charged ions may interact at very low relative velocities in a cryogenically cooled and ultrahigh vacuum environment.

The system studied in the thesis is a particle in a two-dimensional box on the surface of a sphere with constant radius. The different systems have different radii while the box dimension is kept the same, so the curvature of the surface of the box is different for the different systems. In a system with a sphere of a large radius the surface of the box is almost flat. What happens if the radius is decreased and the symmetry is broken? Will the system become chaotic if the radius is small enough? There are some properties of the eigenfunctions, that show different things depending on whether the system is chaotic or regular. The  amplitude distribution of the probability density, the amplitude distribution of the eigenfunction and the probability density look different for chaotic and regular systems. The main subject of this thesis is to study these distributions.

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