Substitutional dopants in III-V semi-conductors, such as Si atoms in GaAs, are of great interest for the applications in transistors, Schottky diodes, and doping super-lattices which have been widely employed to control the electrical properties of semi-conductors. Although Si doped GaAs systems have been intensively investigated theoretically and experimentally in the last several decades, some properties are still debated. In order to give a further explanation of Si doped GaAs systems, we systematically studied DX center in bulk GaAs and in GaAs(110), as well as the relative stabilities of different charged systems for Si atom replacing Ga atom at the substitutional site near GaAs(110) surface from first principles ground state method. We show that DX centre is a metastable state in bulk GaAs and completely unstable in the top few layers of GaAs(110). When Si atom replaces Ga atom at the surface, Charge states have an important influence on the stability of the system, and the additional charge is mainly concentrated on the Si atom for charged system. In addition, we studied the STM images of clean GaAs(110) and charged Si:GaAs(110) by employing Tersoff-Hamann approximation. The calculated STM images are in good agreement with experimental results. We show that at the positive bias voltage the positively charged Si atom presents a bright feature while the negatively charged Si atom shows a dark feature. In a semi-conductor, all bands are either completely full or completely empty. It is well known that DFT underestimates the band gaps of semi-conductors, a simple rigid shift can be used to correct the band energies of semi-conductors. Unlike semi-conductor, the fermi energies of metals lie in some bands. Furthermore, it turned out that some noble metals such as Cu and Ag depend on the considered band and k point , therefore, the so-called scissors operator can not be used for the metallic systems. The most successful approach within theoretical method for these metals is the many body perturbation theory. On the other hand, an interesting study for metals is quasi-particle excitations, which play an important role in a rich variety of physical and chemical phenomena such as energy transfer in photochemical reaction, desorption and oxidation of molecules at surfaces, spin transport within bulk metals, across interfaces, and at surfaces. One of the crucial properties of quasi-particle excitation is their lifetimes which determine the duration of these excitations. We carried out the calculations of quasi-particle band-structures and lifetimes for noble metals Cu and Ag within the GW approximation. For Cu, both the calculated positions of the d bands and the width of the d bands is within 0.1 eV compared to the experimental results. For Ag, partial core correction should be included in the pseudo-potential to get reliable positions of the d bands. The calculated lifetime agree with the experiment in the energy region away from the Fermi level, but deviates from the experimental results near the Fermi level where short range interactions which GW approach fails to describe play an important role. For a better description of the lifetime near the Fermi level, higher terms beyond the GW approximation in the many body perturbation theory need to be considered. In addition, the image potential state lifetimes in Cu(100) have been calculated using GW approximation based on the localized Gaussian basis set, and the calculated n=1, 2 imagepotential state lifetimes are in good agreement with experimental results.

Die vorliegende Dissertation untersucht den Wandel der sozialen Beziehungen zwischen Gutsherren, Instleuten, Bauern und unterbäuerlichen Schichten im Samland nach der "Bauernbefreiung". Vor dem Hintergrund soziologischer Konzeptionen von Macht und Herrschaft und philosophischer Theorien zu Freiheit und Gleichheit, wird der Verlauf dieser Beziehungen vom Feudalismus bis in die Neuzeit nachgezeichnet. Der Fokus dieser Arbeit liegt auf den gesellschaftlichen Folgen der "Bauernbefreiung", denn durch die Aufhebung der Leibeigenschaft und Ablösung der Dienstpflichten entwickelte sich eine neue Gesellschaftsschicht: die Klasse der Landarbeiter.

I present and discuss the results of calculations ofelectronic structures of perfect and defective CaF2 and BaF2 crystals. These are based on the ab initio Hartree-Fock method with electron correlation corrections and ondensity-functional theory calculations with different exchange-correlation functionals, including hybrid exchange techniques.The defective systems include F centers, M centers, O-V dipoles, Hydrogen impurities and H centers.

No description available.

In dieser Arbeit setzen wir ab-initio-Methoden zur Untersuchung einiger Oberflächensysteme und eines Bulksystems ein. Im Wesentlichen greifen wir hierbei auf die Dichtefunktionaltheorie (DFT) und die GW-Approximation (GWA) im Rahmen der Vielteilchenstörungstheorie zurück. Wir nutzen diese Methoden um die Adsorption von TMA auf der Rutil TiO2-Oberfläche zu untersuchen, optische Spektren von TiO2 zu berechnen und um die Adsorption von [7]-HCA auf der Calcit(10-14)-Oberfläche zu verstehen. Weiterhin beschäftigen wir uns intensiv mit PTCDA auf Ag(111), welches mit einer chemisch kontaktierten STM-Spitze manipuliert wird.

The ability of physics to provide an understanding of our Universe lies in the essential interrelation between experiment and theory. But physics does not provide us only reliable representations of the causes acting in nature. Its powerful experimental devices and theoretical methods are the underlying reason of the explosive technological development of our time. LiNbO3 and LiTaO3 represent only one example of the essential impact of both experimental and theoretical investigations on their technological applications. Particularly, LiNbO3 has been the subject of many experimental studies due to its applications in electro-optic and integrated optical devices. Also, the doped LiNbO3 with rare-earth and transition metals could be used, for instance, as a material for tunable lasers. The previous theoretical studies devoted to LiNbO3 and LiTaO3 focused on their electronic structure, being an attempt to understand the microscopic origin of the paraelectric-to-ferroelectric phase transition of these materials. The ab initio lattice dynamics investigations performed so far were mainly aimed to identify the role of the individual atoms vibrations in the energetic of the phase transition. The lack of a reliable model for the zone-center lattice dynamics in these compounds motivated us to investigate this issue by means of ab initio frozen-phonon calculations. On the background of the obtained phonon frequencies and eigenvectors, we unambiguously identified all zone-center modes for LiNbO3 and the A1 ones for LiTaO3. Due to the above mentioned enlargement of the technological applications of LiNbO3 by doping with various ions, we focused on the analysis of the ground-state properties of this material when doped with Fe and Cr. Even if the theoretical approach used in our calculations is not predictive with respect to the optical properties of the physical systems in study, a certain insight on this problem could be gained from the analysis of the effect of the atomic positions relaxation on the impurities energy levels localized in the optical band gap.

The presented thesis includes investigations to fully characterize the electronic structure and magnetic properties ofselected manganese containing high-spin molecules by means of various X-ray spectroscopic, magnetic and theoretical methods. The investigations on the Mn4 star-shaped molecule havelead to a number of interesting results. Magneto-chemical studies exhibit very weak exchange coupling constantsbetween the four Mn(II) ions, leading to complicated low lying states in which the ground state is not well separated, resulting from a dominant weak ferromagnetic coupling and a giant moment of up to 20 µB/f.u. XMCD measurements revealed that almost the completemagnetic moment is located around the Mn(II) ions.This is in agreement with only a few charge transfer states foundwithin the detailed X-ray absorption spectroscopic study. The electronic structure and detailed magnetic properties of the star-shaped heteronuclear CrIIIMnII3 complex have been precisely investigated.With XPS the homovalency of Mn and Cr have been verified. The XA-spectra of the manganese and chromium L edges were measured and compared to earlier investigated Mn4 spectra.The combination high-magnetic field magnetic measurements and element selective XMCD of Mn and Cr L edges and quantum model calculations lead to a complete analysis of the magnetic structure of the CrMn3 magnetic core. The III valence state of the manganese ions in MnIII6O2Salox has been verified. From X-ray diffraction, typical Jahn-Teller distorted oxygen octahedra have been found for Mn(III) ions. Comparisons of XPS and XAS spectra of the complex to corresponding spectraof maganite and tetranuclear manganese(II) cluster it was definitely possible to identify MnIII6O2Salox as a pure Mn(III) compound.