Laser-induced few-body quantum dynamics beyond the mean-field and Born-Oppenheimer approximations
Zusammenfassung der Projektergebnisse
Time-dependent density functional theory (TDDFT) offers an — in principle — exact and feasible alternative to the impossible ab initio solution of the multi-particle timeo dependent Schrödinger equation for a strongly driven many-body system. The fundamental theorems of TDDFT ensure that the wave function and thus every observable is uniquely defined by the one-particle density, which may be determined with the help of an auxiliary system of noninteracting particles (Kohn-Sham approach), much simpler to simulate. We were able to show the existence of the noninteracting auxiliary system under well-defined assumptions, in that way strengthening the formal foundations of TDDFT. In practice, one not only needs to find approximations to the effective potential governing this auxiliary system but also has to construct functionals for the observables of interest. We could show that the second issue is crucial for the proper description of nonsequential double ionization, where the first emitted electron recollides with the parent ion and kicks out a further electron. Resonant interaction of a laser field with an atom induces Rabi-oscillations. In the case of a correlated few-electron system such a resonant interaction is not well-described within TDDFT by known effective potentials. Surprisingly, TDDFT reproduces the emitted radiation quite well despite the fact that the density never assumes the correct excited state form. We could show that the obvious route to cure this problem, namely a few-level approximation, is inconsistent with TDDFT. We have further derived a new approximation for the effective potential of the auxiliary Kohn-Sham system, which is based directly on the fundamental force-balance equation. Finally, we applied TDDFT to the C60 fullerene and studied recollision-induced plasmon excitation (RIPE). The RIPE process leaves its fingerprint on the spectrum of the emitted radiation, showing that single active electron approaches to such systems are doubtful. On the other hand, it allows the experimental study of collective excitations with far off-resonant lasers. The interaction of strong laser fields with molecules causes electronic and nuclear dynamics beyond the Born-Oppenheimer approximation since the electrons are excited into high-lying bound or continuum states. Moreover, the calculation of kinetic-energy spectra of fragments requires a treatment which retains the information about the outgoing particles. We have developed a technique that employs the canonical basis-state expansion for the outer part of the wave function in order to obtain single-particle equations for the time-evolution. The method has been used to investigate the correlation between photoelectrons and parent ions in molecular ionization. Enhancement of high-energy regions in the electron spectra due to channel closings have been found. This arises because the energy release is distributed over electron energy and vibrational energy of the ion so that with increasing vibrational level, channel closing can occur for the electron. Furthermore, we have applied the multiconfiguration time-dependent Hartree method to the coupled electronic/nuclear motion in laser-driven molecules for the first time. A moderate number of configurations in the expansion is sufficient to reproduce the exact dynanics accurately, showing that the multiconfigurational method is a promising tool for multiparticle dynamics in intense-laser molecule interactions.
Projektbezogene Publikationen (Auswahl)
- Adiabatic Approximation of the Correlation Function in the Density-Functional Treatment of Ionization Processes, Phys. Rev. Lett. 97, 203001 (2006)
F. Wilken and D. Bauer
- Intrinsic channel closing in strong-field single ionization of H2, Phys. Rev. A 77, 041403(R) (2008)
S. Pieper and M. Lein
- Influence of molecular vibration on enhancements in high-order above-threshold ionization of hydrogen molecules, J. Mod. Opt. 55, 2631 (2008)
S. Pieper and M. Lein
- Recollision-Induced Plasmon Excitation in Strong Laser Fields, Phys. Rev. A 78, 033413 (2008)
M. Ruggenthaler, S.V. Popruzhenko and D. Bauer
- Local Hartree-exchange and correlation potential defined by local force equations, Phys. Rev. A 80, 052502 (2009)
M. Ruggenthaler and D. Bauer
- Non-Born-Oppenheimer Dynamics of Hydrogen Molecules in Strong Laser- Fields. Dissertation, Universität Kassel 2009
Stefan Pieper
- On the existence of effective potentials in time-dependent density functional theory, J. Phys. A: Math. Theor. 42, 425207 (2009)
M. Ruggenthaler, M. Penz and D. Bauer
- Rabi Oscillations and Few-Level Approximations in Time-Dependent Density Functional Theory, Phys. Rev. Lett. 102, 233001 (2009)
M. Ruggenthaler and D. Bauer
- Time-dependent density functional theory for intense laser-matter interaction. Dissertation, University of Heidelberg 2009
Michael Ruggenthaler
- Multiconfiguration time-dependent Hartree approach for electron-nuclear correlation in strong laser fields, Phys. Rev. A 81, 063421 (2010)
C. Jhala and M. Lein
