Study of charge, spin and orbital states in novel transiton-metal oxides using x-ray absorption spectroscopy

Transition-metal compounds show a wealth of intriguing properties such as superconductivity, piezoelectricity, giant magnetoresistance, spin and metal-insulator transitions, which are governed by the interplay of charge, spin, and orbital degrees of freedom. The knowledge of their electronic structure is crucial for understanding and predicting the fascinating properties of these often strongly correlated materials. In this thesis x-ray absorption spectroscopy including x-ray magnetic circular dichroism is combined with theoretical calculations to investigate the orbital occupation and orbital ordering of La4Ru2O10, which shows a 4d orbital-ordering transition with spin-gap opening due to spin-singlet formation, and of Ca2RuO4 for which the orbital occupation across phase transitions have been studied. The valence state, spin state and orbital moment has been studied for Ca3Co2O6, which have peculiar step-wise jumps in the magnetization, and in Ca3CoRhO6 and Ca3FeRhO6. For LaMn0.5Co0.5O3 the valence, spin state, magnetic alignment, and magnetocrystalline anisotropy was investigated

Study of Charge, Spin and Orbital States in Novel Transition-Metal Oxides Using X-Ray Absorption Spectroscopy

Transition-metal compounds show a wealth of intriguing properties such as superconductivity, piezoelectricity, giant magnetoresistance, spin and metal-insulator transitions, which are governed by the interplay of charge, spin, and orbital degrees of freedom. The knowledge of their electronic structure is crucial for understanding and predicting the fascinating properties of these often strongly correlated materials. In this thesis x-ray absorption spectroscopy including x-ray magnetic circular dichroism is combined with theoretical calculations to investigate the orbital occupation and orbital ordering of La4Ru2O10, which shows a 4d orbital-ordering transition with spin-gap opening due to spin-singlet formation, and of Ca2RuO4 for which the orbital occupation across phase transitions have been studied. The valence state, spin state and orbital moment has been studied for Ca3Co2O6, which have peculiar step-wise jumps in the magnetization, and in Ca3CoRhO6 and Ca3FeRhO6. For LaMn0.5Co0.5O3 the valence, spin state, magnetic alignment, and magnetocrystalline anisotropy was investigated

Time-dependent electron localization function

The electron localization function ELF, which is crafted to reveal chemical bonds and their properties, has been generalized to the time-dependent regime. This allows the time-resolved visualization of the formation, modulation and breaking of bonds and gives thus insight into the dynamics of excited electrons. This has been illustrated by the pi–pi* transition of ethyne induced by a laser field, and by the destruction of bonds and the formation of lone-pairs in a scattering process of a proton with ethene. In the second part, an optimal control algorithm is used to determine an optimized laser pulse of a HOMO–LUMO transition of the diatomic molecule lithium fluoride

Libxc: a library of exchange and correlation functionals for density functional theory

The central quantity of density functional theory is the so-called exchange-correlation functional. This quantity encompasses all non-trivial many-body effects of the ground-state and has to be approximated in any practical application of the theory. For the past 50 years, hundreds of such approximations have appeared, with many successfully persisting in the electronic structure community and literature. Here, we present a library that contains routines to evaluate many of these functionals (around 180) and their derivatives.Comment: 15 page

FLEUR

FLEUR is an all-electron DFT code based on the full-potential linearized augmented plane-wave method (FLAPW). It is mainly developed at the Forschungsentrum Jülich, Germany and available for the materials research community