Separating different contributions to the crystal-field parameters using Wannier functions.

We discuss the calculation of crystal-field splittings using Wannier functions and show how contributions to the crystal-field splitting that are due to hybridization with different ligand states can be separated from the bare Coulomb contribution by constructing sets of Wannier functions incorporating different levels of hybridization. We demonstrate this method using SrVO3 as a generic example of a transition metal oxide. We then calculate trends in the crystal-field splitting for two series of hypothetical tetragonally distorted perovskite oxides and discuss the relation between the calculated 'electrostatic' contribution to the crystal field and the simple point charge model. Finally, we apply our method to the charge disproportionated 5d electron system CsAuCl3. The proposed procedure elucidates the way in which the negative charge transfer energy in this material leads to a reversal of the p-d ligand contribution to the crystal-field splitting such that the eg states of the nominally Au(3+) cation are energetically lower than the corresponding t2g states.

Maximally localized Wannier functions in LaMnO3 within PBE + U, hybrid functionals and partially self-consistent GW: an efficient route to construct ab initio tight-binding parameters for eg perovskites.

Using the newly developed VASP2WANNIER90 interface we have constructed maximally localized Wannier functions (MLWFs) for the e(g) states of the prototypical Jahn-Teller magnetic perovskite LaMnO(3) at different levels of approximation for the exchange-correlation kernel. These include conventional density functional theory (DFT) with and without the additional on-site Hubbard U term, hybrid DFT and partially self-consistent GW. By suitably mapping the MLWFs onto an effective e(g) tight-binding (TB) Hamiltonian we have computed a complete set of TB parameters which should serve as guidance for more elaborate treatments of correlation effects in effective Hamiltonian-based approaches. The method-dependent changes of the calculated TB parameters and their interplay with the electron-electron (el-el) interaction term are discussed and interpreted. We discuss two alternative model parameterizations: one in which the effects of the el-el interaction are implicitly incorporated in the otherwise 'noninteracting' TB parameters and a second where we include an explicit mean-field el-el interaction term in the TB Hamiltonian. Both models yield a set of tabulated TB parameters which provide the band dispersion in excellent agreement with the underlying ab initio and MLWF bands.

A strain-driven morphotropic phase boundary in BiFeO3.

Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.

Electrical control of antiferromagnetic domains in multiferroic BiFeO3 films at room temperature.

Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. In this work, we demonstrate the first observation of electrical control of antiferromagnetic domain structure in a single-phase multiferroic material at room temperature. High-resolution images of both antiferromagnetic and ferroelectric domain structures of (001)-oriented multiferroic BiFeO3 films revealed a clear domain correlation, indicating a strong coupling between the two types of order. The ferroelectric structure was measured using piezo force microscopy, whereas X-ray photoemission electron microscopy as well as its temperature dependence was used to detect the antiferromagnetic configuration. Antiferromagnetic domain switching induced by ferroelectric polarization switching was observed, in agreement with theoretical predictions.

[Diagnostic assessment and documentation of psychosomatic diseases]. / Diagnosefindung und Dokumentation psychosomatischer Erkrankungen.

Besides the notion of psychosomatic medicine as a way of viewing, there is need of a definition of so-called psychosomatic diseases from the aspect of demarcation against general bio-psycho-social interactions. To this end, evidence of a framework of conditions has to be provided which integrates organopathological, experience-related psychological and social parameters. The traditional medical history must be broadened to cover these connections and for this purpose an orientation system is presented.