Top Curr Chem (2016) 368: 219–272
DOI: 10.1007/128_2014_616
# Springer International Publishing Switzerland 2015
Published online: 10 April 2015
Dynamical Processes in Open Quantum
Systems from a TDDFT Perspective:
Resonances and Electron Photoemission
Ask Hjorth Larsen, Umberto De Giovannini, and Angel Rubio
Abstract We present a review of different computational methods to describe
time-dependent phenomena in open quantum systems and their extension to a
density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative
processes. Initially we analyze the concept of an electronic resonance, a central
concept in spectroscopy associated with a metastable state from which an electron
eventually escapes (electronic lifetime). Resonances play a fundamental role in
many time-dependent molecular phenomena but can be rationalized from a timeindependent context in terms of scattering states. We introduce the method of
complex scaling, which is used to capture resonant states as localized states in the
spirit of usual bound-state methods, and work on its extension to static and timedependent density-functional theory. In a time-dependent setting, complex scaling
can be used to describe excitations in the continuum as well as wave packet
dynamics leading to electron emission. This process can also be treated by using
open boundary conditions which allow time-dependent simulations of emission
processes without artificial reflections at the boundaries (i.e., borders of the simulation box). We compare in detail different schemes to implement open boundaries,
namely transparent boundaries using Green functions, and absorbing boundaries in
A.H. Larsen (*) and U. De Giovannini (*)
Nano-bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF),
Centro de Fı ´sica de Materiales CSIC-UPV and DIPC, Universidad del Paı ´s Vasco UPV/EHU,
E-20018 Donostia–San Sebastia ´n, Spain
e-mail: asklarsen@gmail.com; umberto.degiovannini@gmail.com
A. Rubio (*)
Nano-bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF),
Centro de Fı ´sica de Materiales CSIC-UPV and DIPC, Universidad del Paı ´s Vasco UPV/EHU,
E-20018 Donostia–San Sebastia ´n, Spain
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
e-mail: angel.rubio@ehu.es
DOI: 10.1007/128_2014_616
# Springer International Publishing Switzerland 2015
Published online: 10 April 2015
Dynamical Processes in Open Quantum
Systems from a TDDFT Perspective:
Resonances and Electron Photoemission
Ask Hjorth Larsen, Umberto De Giovannini, and Angel Rubio
Abstract We present a review of different computational methods to describe
time-dependent phenomena in open quantum systems and their extension to a
density-functional framework. We focus the discussion on electron emission processes in atoms and molecules addressing excited-state lifetimes and dissipative
processes. Initially we analyze the concept of an electronic resonance, a central
concept in spectroscopy associated with a metastable state from which an electron
eventually escapes (electronic lifetime). Resonances play a fundamental role in
many time-dependent molecular phenomena but can be rationalized from a timeindependent context in terms of scattering states. We introduce the method of
complex scaling, which is used to capture resonant states as localized states in the
spirit of usual bound-state methods, and work on its extension to static and timedependent density-functional theory. In a time-dependent setting, complex scaling
can be used to describe excitations in the continuum as well as wave packet
dynamics leading to electron emission. This process can also be treated by using
open boundary conditions which allow time-dependent simulations of emission
processes without artificial reflections at the boundaries (i.e., borders of the simulation box). We compare in detail different schemes to implement open boundaries,
namely transparent boundaries using Green functions, and absorbing boundaries in
A.H. Larsen (*) and U. De Giovannini (*)
Nano-bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF),
Centro de Fı ´sica de Materiales CSIC-UPV and DIPC, Universidad del Paı ´s Vasco UPV/EHU,
E-20018 Donostia–San Sebastia ´n, Spain
e-mail: asklarsen@gmail.com; umberto.degiovannini@gmail.com
A. Rubio (*)
Nano-bio Spectroscopy Group and European Theoretical Spectroscopy Facility (ETSF),
Centro de Fı ´sica de Materiales CSIC-UPV and DIPC, Universidad del Paı ´s Vasco UPV/EHU,
E-20018 Donostia–San Sebastia ´n, Spain
Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany
e-mail: angel.rubio@ehu.es