[ Funding ]
[ Collaborations ]
Photo - and STM- induced chemistry at surfaces
Photo- and STM- (Scanning Tunneling
Microscope) induced processes
at surfaces are important and interesting for applications (microstructuring
of materials, surface photo- and femtochemistry, photocontrol,
single molecule manipulation), and for fundamental reasons
(treatment of 'open', driven quantum systems
in contact with a 'bath'
of surrounding modes). Using
quantum dynamical (open-system density matrix theory,
wave packet propagation) and quantum chemical methods,
the following topics / reactions are investigated (for
a review, see ):
- Photodesorption of atoms and small
molecules from metal surfaces [12,15,20,21,22,24,25,29,30,35,42,43,45,46,47,54].
desorption of atoms and molecules from semiconductor
and metal surfaces [36,40,47,53].
- Laser control of surface chemical
- Quantum chemistry of photo- /STM-active
Atom and molecule scattering at surfaces
The elastic, inelastic,
and reactive scattering of atoms and
molecules from rigid and nonrigid surfaces is important for
the understanding of heterogeneous catalysis. Here we
develop, test, and apply various time-independent and time-dependent
quantum scattering methods to treat scattering of
atoms and molecules at metal surfaces. Specific examples are:
- Time-independent reactive scattering
and rate theory for the dissociative sticking
of diatomic molecules at rigid metal surfaces
- Development and application of wavepacket
methods for the scattering of atoms and molecules at rigid
and nonrigid metal surfaces [23,31,33,41,44,45].
- Development and application of open-system
density matrix based methods for gas-surface
The quantum mechanical
description of (laser-driven) electron dynamics
in molecular and solid-state systems is of relevance for
molecular and nanoelectronics, photochemistry, and spectroscopy
at interfaces. Here,
explicitly time-dependent methods (open-system density
matrix theory and / or time-dependent density functional theory)
are used to describe:
- The pump-probe spectroscopy of image
charge states at a Cu surface .
- The laser-driven electron transport
through metal-insulator-metal contacts (to be
is a useful alternative to experiment:
Not only is the assignment of spectroscopical lines
to specific state-to-state transitions easily possible, but
also environmental and temperature effects can be modelled
in some detail. We use quantum chemical ab initio methods
or quantum dynamical techniques to evaluate spectroscopical signals
of isolated and embedded molecular species. Specific examples
- Time-independent and time-dependent
(wavepacket) calculation of electronic and /
or vibrational spectra of isolated molecular systems
- Time-dependent open-system density
matrix theory of electronic and / or vibrational
spectra of large molecules or molecules embedded in
an environment [18,39,50,51].
chemical characterization of electronically excited states
of biomolecules using CI, DFT-CI, and TD-DFT and MR-MPn methods
(to be published).
Electronic structure of molecules and solids
The electronic structure
of molecules and solids in their ground
and excited states is investigated with the help of
ab initio methods. Standard programs such as GAUSSIAN98, CRYSTAL,
and CASTEP are used for this purpose. Examples are:
- The electronic structure of ceramic
High-T_c superconductors using ab initio cluster
and band structure calaculations [3,4,6,9].
- Electronic structure of low-dimensional
a. Polymers .
b. 'Gap engineering' in layered materials .
c. 'Quantum size effects' in metal films [8,49].
structure of molecules in ground and electronically excited
Tools of molecular and solid state quantum mechanics are developed
/ improved for the modelling and understanding of the structure
and dynamics of moleculer systems, either isolated or in contact
with an environment. Examples are:
- Electronic structure theory:
a. Self-consistent treatment of long-range Coulomb interactions
in solids .
b. Implementation of scalar-relativistic effective core potentials
in periodic Hartree-Fock schemes [1,2].
- Condensed phase dynamics:
a. Development / improvement of methods for the solution of open-system
Lioville- von Neumann equations [21,26,29,32,35,39,48].
b. Methods / concepts of calculating lifetimes of vibrationally
or electronically excited atoms or molecules in an environment
c. Test / development / improvement of time-dependent wave packet
and quantum-classical methods for scattering of atoms and molecules
at non-rigid surfaces [23,33,41,44]