Computational Materials Science
PD Dr. Thomas Gruhn
Theory group leader
Inverse Design of Glasses and Polymer Materials
Materials with specific properties, like a high Curie temperature or superconductivity, are often found accidentally in the lab by measuring new types of materials. Standard computational approaches follow the same strategy by computing a given material and measuring the properties of interest. The inverse design goes in the opposite direction. It starts with the desired material properties and designs the corresponding material. The method is well established for regular solids like crystalline semiconductors. We develop a novel inverse design method for materials without long-range order like glass or polymer systems.
CIGS Thin-film solar cells
Solar cells based on chalcopyrite absorbers like Cu(In,Ga)Se2 (CIGS) show the highest efficiency of all thin film solar cells. Nevertheless, the current efficiency world record is far below the theoretical limit. With the help of DFT-based calculations and computer simulations we optimize CIGS cells in two ways: (a) We study the structure and consequences of defects, disorder, and impurity diffusion in the absorber material to find new strategies for optimizing the efficiency of the cell. (b) We investigate new material classes like 8-electron half-Heusler materials in order to find a new buffer layer material that is free of the toxic element cadmium.
Systems of Rod-like Macromolecules and Filament Networks
Rod-like macromolecules like carbon nanotubes are of great relevance for the creation of nanostructures. Carbon nanotubes are used for electrical nano-circuits, nano-transistors, biosensors and other applications. Using Monte Carlo methods, we study structures formed in systems of mono- and polydisperse spherocylinders in the bulk and in contact with substrates. An important aspect are attractive depletion forces that become relevant if polymers are added to the solvent. Ultra-porous three-dimensional networks may form reversibly in a system of chemically heterogeneous rods with attractive end groups. Beside others, we have performed Monte Carlo simulations of a system of hard spherocylinders that can be connected by short rod-like cross-linkers. This way we have a simple model system of an actin network. In living cells, actin networks are part of the cytoskeleton which influences the cell shape and serves as a transport system.
Fluid Vesicles
Vesicles are closed shells of lipid membranes, which are created in living cells but can also be synthesized in the laboratory where they serve as simple models for cells. With Monte Carlo simulations we investigate shape, adhesion, and transport properties of fluctuating vesicles. The pharmaceutically relevant transport of drug-loaded vesicles through skin pores has been analyzed and a simple method for measuring the adhesion strength of vesicles has been derived which was successfully tested experimentally.
Stanislav Shadov
Spintronics, Superconductivity, Topological InsulatorsMy research interests are guided by theoretical aspects of the materials science, i.e. by modeling new materials and studying, analyzing and optimizing their material properties. Since all this finally links to the electronic structure, the most extensively used instrument here are the band structure methods. Currently, my activity is mainly focused on spintronic applications. This includes ab-initio modeling of the effective TMR and GMR based systems, materials for the spin-torque based MRAM, research on topological insulators (realization of the Quantum Spin Hall effect). Furthermore, strongly-correlated electron systems and high-temperature superconductivity are integral parts of my research interests, as well.
To top of pageJanos Kiss
Defect Structures in Solar CellsOur research interest is the investigation of physical and chemical properties in the field of theoretical material and surface science using ab-initio methods based on density functional theory. In the frame of our current research activity we are focusing on two main topics. These are the interaction of graphene with silicon surfaces and the formation of various defect structures and vacancy diffusion processes in thin film absorber materials employed in solar cells. For the study of structural and dynamic properties we perform ab-initio total energy calculations and molecular dynamics simulations using the Car-Parrinello technique combined with metadynamics. The calculations are carried out with the CPMD and Quantum-Espresso program packages, which are highly efficient parallelized electronic structure and molecular dynamics codes based on plane-waves and pseudo-potentials.
Shahab Naghavi
Correlated SystemsMy project is focused on electronic structure calculations of correlated systems. Correlated molecular and periodic systems are studied with various numerical ab initio methods. One system of interest are charge transfer salts based on disk-shaped polycyclic aromatic hydrocarbons like coronene derivatives. In addition, correlated periodic systems like Rb4O6 and FeSe are studied. For correlated systems, standard DFT methods using LDA or GGA approximation often fail, while hybrid functionals like B3LYP provide reasonable results.
Christian Ludwig
Absorber Material CIGSThe absorber material of CIGS thin-film solar cells is studied in collaboration with IBM. We perform Monte Carlo simulations to investigate the phase diagram and inhomogeneities in the disordered phase of Cu(In,Ga)Se2. To calculate configuration energies, a cluster expansion based on ab initio electronic structure calculations is used.
Stephan Rix
Point Defects in CaF2Stephan Rix is currently working on his PhD thesis with the topic “Point defects in calcium fluoride and their effects on the optical properties under 193 nm radiation”. The focus of his work is to understand radiation damage mechanisms on a microscopic level. He uses density functional methods to calculate defect properties. The formation of point defects by radiation and the stability of these radiation-induced defects are of special interest. Furthermore, he investigates the diffusion properties of point defects and their long-term stabilization within the bulk material.
Stephan Rix’s work is supported by SCHOTT AG and the Graduate School of Excellence Materials Science in Mainz (MAINZ).
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