Research Projects

Research Projects

The computational design of high strength steels such as FeMn alloys often faces a combination of challenges: (1) the treatment of chemical complexity, (2) the treatment of magnetic disorder, in particular, in the paramagnetic state, and (3) the treatment of structural defects. Moreover, the interplay of these degrees of freedom also needs to be accounted for. In this project we particularly focus on this kind of coupling of different degrees of freedom, since we believe it is decisive to understand some of the phenomena observed in FeMn alloys.

Coupling of degrees of freedom in FeMn steels

The computational design of high strength steels such as FeMn alloys often faces a combination of challenges: (1) the treatment of chemical complexity, (2) the treatment of magnetic disorder, in particular, in the paramagnetic state, and (3) the treatment of structural defects. Moreover, the interplay of these degrees of freedom also needs to be accounted for. In this project we particularly focus on this kind of coupling of different degrees of freedom, since we believe it is decisive to understand some of the phenomena observed in FeMn alloys. [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.

Spin-lattice coupling

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]
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.

Ab initio up to the melting point: Anharmonicity and vacancies in aluminum

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 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.

Planar defects in off-stoichiometric, Nb-rich NbFe2 Laves phase

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]
The thermodynamic stability of computationally designed multicomponent compounds against decomposition into structures with less favorable properties is often unclear. In this project, we have used sophisticated finite temperature ab initio methods to determine the relative phase stabilities of promising Ce-Fe-Ti hard-magnetic materials.

Hard-magnetic materials

The thermodynamic stability of computationally designed multicomponent compounds against decomposition into structures with less favorable properties is often unclear. In this project, we have used sophisticated finite temperature ab initio methods to determine the relative phase stabilities of promising Ce-Fe-Ti hard-magnetic materials. [more]
Al-based alloys are promising structural materials owing to their mechanical properties and high thermal stability complemented by their light weight. Their performance and stability, however, is largely governed by the properties of inherent second phase particles. Computationally designing technologically-relevant alloys with desired properties therefore requires a comprehensive knowledge of the underlying atomistic processes and the interplay of strain and chemistry. The aim of this project is to integrate theory and experiments in understanding the thermodynamic and kinetics aspects of thermo-mechano-chemical coupling during the precipitate formation in Al-based alloys taking the example of Al-Sc and Al-Sc-Zr systems.

Thermo-mechano-chemical coupling during precipitate formation in Al-based alloys

Al-based alloys are promising structural materials owing to their mechanical properties and high thermal stability complemented by their light weight. Their performance and stability, however, is largely governed by the properties of inherent second phase particles. Computationally designing technologically-relevant alloys with desired properties therefore requires a comprehensive knowledge of the underlying atomistic processes and the interplay of strain and chemistry. The aim of this project is to integrate theory and experiments in understanding the thermodynamic and kinetics aspects of thermo-mechano-chemical coupling during the precipitate formation in Al-based alloys taking the example of Al-Sc and Al-Sc-Zr systems.
[more]
The aim of this project is to resolve the interplay of real space structure and electronic states in combination with magnetic disorder for iron-based superconductors.  We apply a combination of density-functional theory calculations and effective tight-binding models for the electronic energy dispersion. This allows us to connect direct influences of magnetism and structural changes, like pressure, lattice distortions, vacancies and spin-orbit coupling, with the superconducting properties. With these approaches we determined the superconducting ground state of a recently discovered new structure family of the iron-based superconductors.

Ab initio design of iron-based high-temperature superconductors

The aim of this project is to resolve the interplay of real space structure and electronic states in combination with magnetic disorder for iron-based superconductors.  We apply a combination of density-functional theory calculations and effective tight-binding models for the electronic energy dispersion. This allows us to connect direct influences of magnetism and structural changes, like pressure, lattice distortions, vacancies and spin-orbit coupling, with the superconducting properties. With these approaches we determined the superconducting ground state of a recently discovered new structure family of the iron-based superconductors.
[more]
Hydrogen embrittlement (HE) 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.

Scale bridging modelling of hydrogen embrittlement

Hydrogen embrittlement (HE) 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]
Understanding hydrogen-assisted embrittlement of advanced high-strength steels is decisive for their application in automotive industry. Ab initio simulations have been employed in studying the hydrogen trapping of Cr/Mn containing iron carbides and the implication for hydrogen embrittlement.

Hydrogen-carbide interaction

Understanding hydrogen-assisted embrittlement of advanced high-strength steels is decisive for their application in automotive industry. Ab initio simulations have been employed in studying the hydrogen trapping of Cr/Mn containing iron carbides and the implication for hydrogen embrittlement. [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.

Mechanisms of self and impurity diffusion in Fe-Al intermetallic compounds

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]
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.

Ab initio based description of the stacking fault properties in high-Mn steels

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. [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.

Ab initio study on the coupling of lattice and magnetic degrees of freedom and the role of interfaces in magneto-caloric materials

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]
Complex simulation protocols combine distinctly different computer codes and have to run on heterogeneous computer architectures. To enable these complex simulation protocols, the CPS group contributes to the development of pyiron.

pyiron - an integrated development environment (IDE)
for computational materials science

Complex simulation protocols combine distinctly different computer codes and have to run on heterogeneous computer architectures. To enable these complex simulation protocols, the CPS group contributes to the development of pyiron. [more]
 
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