Projects and Collaborations
Collaborative Research Centre 'Non-Equilibrium Dynamics of Condensed Matter in the Time Domain' (SFB 1242)
Project B2: Ab-Initio Simulation of Electronic Excitation and Relaxation
This project will be mainly concerned with the simulation of sub-picosecond dynamics in low-dimensional systems, i.e., in molecules, or in layers of two-dimensional materials. The systems to be studied are stimulated on a femtosecond time scale by an ultra-short laser pulse or by ion impact. Topics of interest are both the frequency-dependent optical response of the system as well as the interplay of its numerous internal degrees of freedom (of the atomic coordinates, charge and spin
state) in response to the excitation. We will focus on systems where the forces due to electronic excitations are very strong, such that they can switch the atomic geometry between the ground state and a long-lived non-equilibrium state. A similar process occurs locally at an electronically driven phase transition at a surface, e.g. on the Si(100) surface. The methods used to simulate the dynamics comprise time-dependent density functional theory (TDDFT) combined with Ehrenfest dynamics, employing a computer code based on atom-centred numerical orbitals that allows for an efficient numerical treatment of system with low dimensionality and low symmetry.
Project B7: Unifying Theoretical Description of Relaxation in Electron Systems
The excitation of an electron system on ultrashort time scales, e.g. by femtosecond laser pulses, triggers complex many-body dynamics. The dominating relaxation mechanisms may vary depending on the time passed since the excitation and the relevant coupling strengths. It is the aim of this project to develop a comprehensive picture of these relaxation phenomena by intertwining different theoretical approaches. This will be achieved by method development at the interfaces between them. The developed theory will ignificantly enhance our general understanding of non-equilibrium dynamics and will provide the basis for the interpretation of pump-probe experiments.