Research Areas

(A) Calculation of electronic states and transitions using many-particle methods

This work aims at the precise ab initio calculation of electronic excitation energies and intensities in the field of photoabsorption and photoemission, photoionization and the Auger decay of molecules . ^1-3) Besides the application of conventional quantum chemical methods, the main interest focuses on the application and development of field-theoretical many-particle methods. ^4,5)

(B) Spectroscopy and radiationless relaxation of polyatomic molecules

Primary interest in this work is the investigation of strong non-Born-Oppenheimer effects. Research focuses especially on a microscopic understanding of ultrafast radiationless decay processes of electronically excited states of molecules and molecular ions . ^6,7) Recently an innovative method was proposed which allows the efficient ab initio calculation of the elements of the coupling matrix required in these studies . ⁸⁾

(C) Electron-molecule scattering, photoionization and Auger decay

The first part of this work concentrates on the ab initio calculation of the electron-molecule scattering process . ⁹⁾ Many-particle effects are taken into account using an optical potential . ¹⁰⁾ Applications ¹¹⁾ were performed that include, e.g., studies of the vibrational dynamic that emerges during the scattering process as well as the calculation of rotation-excitation cross sections (rotational rainbows). Closely related to electron scattering are processes such as photoionization ¹²⁾ and the Auger decay decay ¹³⁾ where only one outgoing but no incoming electron are present (so-called half collisions).

(D) Wave packet dynamics

The motion of nuclei that move on Born-Oppenheimer surfaces and experience the influence of coupled potential energy surfaces may be solved either conventionally, i.e. within the time-independent picture or by the propagation of wave packets. For a number of problems, e.g., the study of decaying molecules (photodissociation) the time-dependent approach supercedes the classical one. Besides the study of models ¹⁴⁾ this research has focused on the development of an efficient algorithm used for the wave packet propagation . ¹⁵⁾

(E) Chaos and statistics

This research field comprises classical chaos theory and its influence on corresponding quantum chemical systems. Particularly nice examples are atoms and molecules in strong magnetic fields where a wealth of interesting and new phenomena already has emerged . ^16,17) A classification of the complex spectra and their interpretation by semi-classical considerations is possible from the statistical analysis of the energy levels . ¹⁸⁾

(F) Structure and dynamics of quasi one-dimensional systems

In this project the multi-mode Peierls distortion of quasi one-dimensional systems is studied with special consideration of the internal degrees of freedom of the monomers . ¹⁹⁾ Examplary applications studied in detail are the equilibrium geometry of polydecker sandwich compounds , ²⁰⁾ phonons and non-linear excitations.

(G) Stable multiply-charged anions of isolated small molecules and clusters

This work has focused particular attention on the theoretical evidence for the existence of small multiply-charged negative ions . ²¹⁾ Precise many-particle methods are used in the large-scale calculations required, e.g., for the assessment of the electronic stability of this interesting class of species. Current research focuses on medium-sized to large highly-charged anions of molecules and clusters ²²⁾ as well as on the development of simplified theoretical models that allow for a deeper understanding of the interesting phenomena observed.

(H) Fundamental Aspects, Electronic Structure and Dynamics of Atoms and Molecules in Strong Magnetic Fields

This project includes the investigation of fundamental properties of molecules in strong magnetic fields . ¹⁷⁾ We hereby focus on the separation of the different types of motion, the Born-Oppenheimer approximation in external fields, symmetry properties of molecules in fields etc... The ab initio computation of the electronic structure of many electron systems in strong magnetic fields is also a central aspect of these research activities ²³⁾. Highly excited Rydberg atoms in strong magnetic fields belong to the simplest physical systems which exhibit regular, chaotic as well as intermittent dynamics and serve therefore as a laboratory for the appearance of chaos in simple microscopic quantum systems. Both classical as well as quantum mechanical studies are performed here ²⁴⁾ Due to the nonseparability of the different degrees of freedom the transition from regularity to chaos in the electronic motion shows up also in the center of mass motion.

(I) MCTDHB - Quantum Many-Body Physics with Ultra-Cold Bosons