Finished Projects

This is an unsorted list of older projects.

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. [more]
The effect of surfaces and more specifically of surface reconstruction and rehybridization on the properties, composition, ordering and thermal stability of epitxailly grown alloys is investigated. [more]
III-Nitride alloys such as InN, GaN, and AlN dominate the optoelectronics industry with applications in light emitting devices (LED), laser diodes (LD), and power electronics and constitute one of the most important semiconducting materials nowadays. In this project the bulk thermodynamics of these alloys are investigated. [more]
ZnO is a wide band gap semiconductor which is of interest to such diverse areas of application as passivation layers on steel surfaces, catalysis, corrosion, adhesion, gas sensing, and micro- or optoelectronics. Understanding the surface structure and stoichiometry is of high practical interest and essential for any of the mentioned applications. Keeping in mind that the chemical environment interfacing with the surface plays a decisive role in the stabilisation and atomic structure of the surface reconstruction, we combine density functional theory (DFT) calculations with atomistic thermodynamics to investigate and understand the stability of polar Zn-terminated ZnO(0001) surfaces in dry and humid environment. [more]
Solid-liquid interfaces are at the heart of many problems of practical importance, such as water electrolysis and batteries, photo catalytic water splitting, electro-catalysis, or corrosion. Understanding the structures forming at surfaces of solids immersed in an aqueous electrolyte is, therefore, of particularly high interest. In this project, we investigate the role the liquid environment plays in shaping such structures. We show that solvation effects are highly selective, having little effect on surfaces with metallic character, but largely stabilizing semiconducting structures, particularly those that experience a high electrostatic penalty in vacuum. [more]
Phase stabilities of multicomponent material systems are best simulated with CALPHAD. The underlying databases are mainly obtained from calorimetric measurements, but suffer often from the fact that for certain phases an experimental approach is not feasible or not conclusive. Here, ab initio calculations emerge as an alternative, which is carefully investigated for the Al-Mg-Si-Cu and Al-Sc system within this project. [more]
The grain structure of a polycrystalline material is a primary determinant of its mechanical properties. Careful control of the evolution of this grain structure during the process of recrystallization is required if alloys are to be optimised for their intended engineering applications. If we are to develop accurate meso-scale models of microstrucutural evolution, we will need a good theoretical understanding of the mobility and migration mechanisms of grain boundaries. [more]
Ti alloys are widely used in industry due to their superior properties, such as high strength, corrosion resistance, biological compatibility. Here, we study the substitution energy of Nb in Ti and reveal important consequences for the stability of various (meta)stable phases. [more]
The diffusion mechanisms in ordered binary alloys are more complicated than in materials with only one atom species. Several mechanisms, including, e.g., triple defect jump cycles, have been suggested in the literature. Within this project, we resolve which of them is energetically most favorable in FeAl and use the calculated barriers for large scale simulations. [more]
Combining concepts of semiconductor physics and corrosion science, we develop a novel approach that allows us to perform ab initio calculations under controlled potentiostat conditions for electrochemical systems. The proposed approach can be straightforwardly applied in standard density functional theory codes. [more]
Ab initio methods based on DFT are now routinely used to investigate T=0 K properties. In contrast, finite temperature DFT studies are rare and, in particular, limited to approximations such as the quasiharmonic model. In the present study, we investigate the influence of anharmonic excitations—which correspond to phonon-phonon interactions beyond the simple quasiharmonic picture—on the thermodynamics of Ti and TiNb alloys. [more]
The stability and concentration of extended defects is closely related to their atomic structure, which can already be complex for planar defects in pure elements or chemically ordered phases, such as Laves phases. In the case of multi-component alloys with off-stoichiometric compositions, the chemical degree of freedom adds another level of complexity. Particularly fascinating becomes the interplay of local chemistry and planar defects, however, if defect structures and/or compositions are created that would not be present otherwise. [more]
Hydrogen embrittlement is a persistent mode of failure in modern structural materials. The processes related to HE span various time and spatial scales. Thus we are establishing multiscale approaches that are based on the parameters and insights obtained by accurate ab initio calculations in order to simulate HE at the continuum level. [more]
The balance between different contributions to the high-temperature heat capacity of materials can hardly be assessed experimentally. In this study, we develop computationally highly efficient ab initio methods which allow us to gain insight into the relevant physical mechanisms. Some of the results have lead to breakdown of the common interpretation of temperature dependencies. [more]
The energetics as well as atomistic mechanisms underlying the segregation of impurities at Si grain boundaries (GB) and GB junctions have been investigated. [more]
Local lattice distortion is one of the core effects in complex concentrated alloys (CCAs). It has been expected that the strength CCAs can be improved by inducing larger local lattice distortions. In collaboration with experimentalists, we demonstrated that VCoNi has larger local lattice distortions and indeed has much better strength than the prototypical CrCoNi CCA has. [more]
At finite temperatures lattice vibrations and magnetic fluctuations are coexisting. To study potential coupling effects, a method is required, which considers both, the spin and the lattice degrees of freedom, simultaneously. We develop and implement such a method by combining atomistic spin dynamics with ab initio molecular dynamics. [more]
Magnetic properties of magnetocaloric materials is of utmost importance for their functional applications. In this project, we study the magnetic properties of different materials with the final goal to discover new magnetocaloric materials more suited for practical applications. [more]
In order to explore the possibility of using high entropy alloys (HEAs) for functional applications such as magnetic refrigeration it is necessary to have an in-depth understanding of their magnetic properties. The main goal of this project is to understand and improve the magnetic properties (e.g., saturation magnetization, Curie temperature etc.) in different medium and HEAs. [more]
The aim of this project is the development of a complete first-principles based methodology to study the magneto-caloric effect (MCE) close to the technologically and scientifically relevant regime of first order magneto-structural transitions. [more]
Modern CPUs provide a number of features to increase the computational power. Unfortunately, this increased computing power is often not used in practice, because the CPU can process the data more quickly than the memory can deliver it. To make full use of this enhanced computing power, the existing algorithms need to be revised to better exploit the computing power by exposing hidden parallelism to the CPU and improving the data locality in the data access patterns. We identified key routines in our plane-wave DFT code that offer such tuning opportunities and demonstrate a significant speed-up over standard approaches. [more]
Eutectic Ti-Fe alloys exhibit a high strength (~1000 MPa), excellent ductility, and sufficient corrosion resistance making them promising candidates for numerous aerospace and automotive applications. Dual-phase Fe-Ti eutectics are composed of a rather brittle FeTi intermetallic phase with the B2 structure and a softer and more ductile β-Ti(Fe) alloy with varying Ti concentrations. [more]
We have developed a MO projector scheme to apply Hubbard-U corrections within density-functional theory to molecular orbitals (MOs). [more]
We have extended the sxdefectalign correction scheme to account for charged defects located at surfaces or interfaces. The scheme allows to extrapolate the formation energy of the defect from very small supercells, even if artificial fields in the calculation are sizeable. [more]
Self-healing metallic materials for the practical use are not properly developed despite of their numerous potential applications. We investigate the possibility of designing new self-healing metals by using a hierarchical modeling approach. The present study aims at examining the interaction between nano-cracks and shape memory nano-particles which is an important concept to realize self-heling metals. The knowledge gained from the present study will guide future experimental works. [more]
Go to Editor View