Our joint CM-MU project is aimed at theoretical identification of fundamental materials design limits in bcc Mg-Li alloys for ultra light-weight applications.
The project is aimed at designing new Fe3Al-based alloys that constitute a very promising class of intermetallics with great potential for high-temperature applications. The experimental investigation is complemented in a multi-disciplinary manner with a scale-bridging theoretical approach combing (i) ab initio calculation and (ii) linear-elasticity homogenization techniques to study the integral elastic response of Fe3Al-based polycrystals.
High-Mn-steels are excellent candidates for the next generation of high-strength materials. In such steels the prevailing plasticity mechanism is determined by stacking fault energy. In this study, we aim to develop a generalized first-principles framework that allows temperature- and composition-dependent atomic-scale description of the stacking fault properties, necessary to explore chemical trends, to deliver parameters for mesoscale models, and to identify new routes to optimize high-Mn-steels.
The energetics and dynamics of hydrogen in metals is a central topic of metal research. Due to its connection to hydrogen embrittlement and hydrogen storage it is highly interesting to scientists as well as engineers. In this study, various materials have been examined in order to identify chemical trends for the solubility and mobility of hydrogen.
Electron energy loss spectroscopy (EELS) performed in a transmission electron microscope offers a high spatial (below 1 nm) and energy (below 0.1 eV with state-of-the-art monochromators) resolution. Its subset, electron energy loss near edge structure (ELNES) is known to reflect the electronic structure of materials. However, a comparison with simulated data is needed for interpretation of the experimental ELNES.
GaN based nanowires (NWs) have recently emerged as potential candidates for nanodevice applications. The majority of the reported GaN NWs have their axial direction along the c-axis, while the facets are assumed to consist of non-polar surfaces.
The mobility of the Grain Boundaries (GBs) is a key mechanism which determines the microstructural evolution during growth: It controls the processes of recrystallization, grain growth, phase transformation, and precipitation. Therefore it determines the grain size and subsequently the yield strength in the post grown material.
In group III-nitrides, due to the large lattice mismatch and the stiffness of the material, the quantum dots embedded in the semiconductor matrix are highly strained and the inclusion of nonlinear elastic effects is crucial. However, so far experimental and/or theoretical data on the composition and stress dependence of the elastic constants of AlGaN alloys are still lacking.
Due to the lack of lattice and thermal matched substrates, growth of wurtzite GaN films results typically in high threading dislocation (TD) densities. Since the work by Lester et al. [1] there is a large controversial debate regarding the effect dislocations have on the electronic and optical properties of group III-Nitride based devices.
ScN is a potential alternative to InN: Sc can be more efficiently incorporated (low vapour pressure) and results in lower lattice mismatch with respect to GaN. ScN is a semiconductor with an indirect band gap. Nevertheless, when ScN is alloyed with GaN it can become a direct band gap semiconductor with a wurtzite-like structure.
Ab-initio calculations to study the thermodynamic stability and concentrations of N at/in surfaces and bulks in ternary and quaternary semiconducting material systems, and to explore the significant role of surface kinetics.
Lars Ismer, Tilmann Hickel, and Jörg Neugebauer
Ultra-high manganese steels (typically 15–30 wt.% Mn), in particular so called TWIP and TRIP steels, have recently become important for industrial purposes, e.g. the car industry. They combine high work hardening rates and strength with a good ductility and hence allow to reduce the weight ...
So far, the balance between the contributions to the high-temperature heat capacity could not be assessed due to experimental scatter. In this study, we develop computationally highly efficient ab initio methods which allow to gain insight into the relevant physical mechanisms.
For modern steel design, the accurate prediction of the magnetic free energy in iron is indispensable. In this study we propose a novel integrated ab initio approach including magnetic excitations. The results clearly show the importance and the impact of magnetism for the description of various properties like e.g. the free energy or the heat capacity.
The project aims to study structural and thermodynamical properties of dilute solid solutions by means of microscopic elasticity theory, using parameters from atomistic modeling employing EAM-potentials and ab-initio calculations.
External collaboration with Prof. Bugaev from Max-Planck-Institut für Metallforschung, Stuttgart.
The C++ library S/PHI/nX provides a modular approach to multiscale simulations and an efficient basis for rapid development of computationally highly efficient multiscale algorithms.
Optoelectronic properties of semiconductor quantum dots, wires and wells including strain and built-in potentials are investigated employing the continuum elasticity theory and an eight-band k*p model.
Hydrogen has the ability to penetrate into and arrange itself in metals. This can cause severe problems, e.g. leads to a lowering of the tensile strength of metallic compounds (like steel) through hydrogen embrittlement.
The project aims to study corrosion, a detrimental process with an enormous impact on global economy, by combining denstiy-functional theory calculations with thermodynamic concepts.
Inter-departmental research activity in cooperation with Dr. M. Palm and Dr. F. Stein. The project is focused on the development of novel low-density high-performance alloys, particularly on investigation and interpretation of the volume-composition anomaly detected in Fe-Al alloys.
Joint inter-departmental research in a close collaboration with the department of Prof. Raabe is an example of a theory-guided materials design of novel mechanically bio-inspired materials for human implants.
External collaboration with Prof. Mojmir Sob from Masaryk University in Brno, Czech Republic, is focused on first-principles analysis of different collinear magnetic phases of iron displacively transformed from the bcc into hcp phase.
The difference in solubility of carbon between the austenite and ferrite is the basis for solid solution hardening of steels. The C-solubility is determined by the C-C interaction energy that ...
Grain boundaries (GBs) play a key role in grain growth and recrystallization, and significantly affect the physical and mechanical properties of materials. Therefore, an important topic in materials design is grain boundary engineering, i.e. optimizing the population of GBs with desirable geometry by suitable thermomechanical treatment. To achieve this a deeper understanding and quantification of the interplay between the GB energies with respect to the misorientation of the two grains (3 dimensional phase space) and the inclination of the boundary plane (2 dimensional phase space) are crucial.
Enhancing the brightness of LEDs to meet the increasing demand for energy-efficient high-power light sources requires to go beyond present-day materials' limits. We explore the options for improving p-doping in GaN, a common LED material, by an optimized handling of hydrogen impurities.
The alpha-chitin is one of the most abundant biological materials. Its complex structure results in a low-weight and high-strength material, which make it a favorable system for potential bio-inspired functional materials applications. In order to gather a deeper understanding of the mechanical properties of alpha-chitin, study of the elastic properties of its pure single-crystalline form is crucial.
This is an open position!
The aim of this project is to develop a practical scheme for band offsets in the framework of the GW method.
Hydrogen induced embrittlement of metals is one of the long standing unresolved problems in Materials Science. A hierarchical multiscale approach is used to investigate the underlying atomistic mechanisms.
The fascinating material properties of magnetic shape memory alloys are investigated by exploring their free energy surfaces. The aim is an atomistic knowledge about the stable crystal structures and the low energy transformation paths.
Solar cells made from amorphous silicon can be produced cheaply, but their conversion efficiency quickly drops in operation. We collaborate with experimentalists to identify the responsible microscopic processes with EPR.
This is an open position!
Polyelectrolyte/silicate interactions will be studied at the atomic scale by density-functional theory (DFT) simulations in close cooperation with experimentalists.
In this project, we explore the possibility to generate atomic orbital basis sets that optimally represent the electronic structure of a given material.
The EXX formalism offers an exact treatment of exchange interactions within Kohn-Sham density functional theory, but the computational cost is presently prohibitive for large systems. We work on improving the implementation for use in defect supercells with several dozens of atoms.
PHInaX combines state-of-the-art interactive visualization techniques, heterogenous job submission, and a new general purpose database concept to provide a full featured workbench for multi-physics applications.
We developed new render techniques for interactive scientific visualization in PHInaX. The new interaction elements (gizmos) have full access to the physics and numerics algorithms available in the S/PHI/nX library.
In contrast to conventional database applications, the new general purpose database approach allows changes of the data set structures without modifications of the underlying database design. Based on the flexible workflow mechanisms available in PHInaX proper database relations can now be created fully automatically.
