Interplay of dimensions, intrinsic structure, and external forces
|Structurally inducible metal insulator transition in a Mo6S6 nanowire, from I. Popov, et al., Nano Lett. 8, 4093-4097 (2008).|
As a cross-linking topic, materials with local and non-local structural disorder are theoretically investigated in close cooperation with the experimental studies of the department. Such materials exhibit novel physical functionalities due to their geometric dimensions. To some extent they show anisotropic mechanical, electronic, and magnetic properties, as well as anisotropic transport coefficients, and thus react in a complex manner to external forces, such as mechanical stress, electromagnetic fields, or temperature gradients. Distortions of the ideal structure can significantly modify the properties or even dominate if defects and nanostructures are comparable in size, or if the deviation is sufficiently strong.
|Fermi-surface of Copper (Cu), the color codes the inverse effective mass of the electrons, large/small effective masses are represented in red/blue, from A. Weismann, et al., Science 323, 1190 (2009).|
Current research projects in the field of simulation aim on the development and application of physical modeling approaches for the related materials science topics and their transfer into computer-based calculation. The primary focus of interest is on nano-sized and nano-structured materials, such as molecules, clusters, wires, tubes, films and composites with complex coupled properties. The systems of interest include electrically or magnetically doped semiconductors for microelectronic and nanoelectronic applications, also taking advantage of the spins of the electrons. Particular attention is paid to self-organizing systems and their structural and mechanical properties as a basis for nano-scale electronics. The aim of these developments is a scale-adapted and multi-scale description of material properties under the influence of external factors and their validation in experiments.
Based on microscopic characteristics, we develop schemes to calculate macroscopic solid state properties to be optimized by a computer-aided material design. The following techniques are the basis for our studies: Density functional methods are used to calculate microscopic structural, electronic and magnetic properties. Meso-scale, particle- and grid-based kinetic Monte Carlo simulations are applied to investigate the structure and domain formation in magnetically frustrated or self-organizing systems, which incorporate parameters that are calculated with ab-initio electronic structure methods. A hybrid model was developed, which couples the particle-based kinetic Monte-Carlo scheme directly with the continuum theory based phase-field method to a two-scale modeling method for structural development in multi-phase systems. Furthermore, macroscopic transport coefficients are calculated by quasi-classical methods using the microscopic parameters.