Dynamical Processes in Open Quantum Systems from a TDDFT Perspective: Resonances and Electron Photoemission

Area of Science:

• Computational quantum chemistry
• Theoretical physics
• Spectroscopy

Background:

• Open quantum systems exhibit time-dependent phenomena like electron emission.
• Electronic resonances, metastable states leading to electron escape, are crucial in molecular processes.
• Understanding excited-state lifetimes and dissipative processes is key.

Purpose of the Study:

• To review computational methods for time-dependent phenomena in open quantum systems.
• To extend these methods to a density-functional framework.
• To focus on electron emission processes in atoms and molecules.

Main Methods:

• Review of computational methods for open quantum systems.
• Extension of methods to density-functional theory (DFT).
• Application of complex scaling and open boundary conditions (transparent, absorbing potentials, mask functions) for electron emission simulations.

Main Results:

• Complex scaling captures resonant states and describes continuum excitations and wave packet dynamics.
• Open boundary conditions enable realistic simulations of electron emission without artificial reflections.
• Comparison of different open boundary schemes is detailed.

Conclusions:

• Computational methods, particularly complex scaling and open boundary conditions within DFT, are effective for studying time-dependent electron emission.
• These methods are applicable to excited-state lifetimes and dissipative processes in atoms and molecules.
• The review provides a foundation for calculating advanced spectroscopic properties like time-dependent pump-probe photoelectron spectroscopy.