Excited state photodynamics on semi-empirical and QM/MM grounds

Marius Wanko, wanko@phys.upb.de1, Michael Hoffmann,
hoffmann@phys.upb.de2, Thomas Keal3, Paul Strodel1, Walter Thiel,
thiel@mpi-muelheim.mpg.de4, Thomas Frauenheim,
frauenheim@phys.upb.de5, and Marcus Elstner, m.elstner@dkfz.de6. (1)
Department of Physics, University of Paderborn, Warburger Str. 100,
D-33098 Paderborn, Germany, (2) Department of Physics, Universität
Paderborn, Warburger Str. 100, 33098 Paderborn, Germany, (3) MPI für
Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr,
Germany, (4) Max-Planck-Institut für Kohlenforschung,
Kaiser-Wilhelm-Platz 1, D-45470, Mülheim an der Ruhr, Germany, (5)
Bremen Center for Computational Materials Science, Bremen University,
Bibliothekstrasse 1, Bremen, 28359, Germany, (6) Theoretical
Chemistry, TU Braunschweig, Hans-Sommer-Straße 10, 38106 Braunschweig,
Germany

The ultrafast dynamics of photo-excited molecular systems is still a
young branch of photochemistry. The enormous progress in
fs-spectroscopy has gained new insights in the formation of excited
state intermediates and radiationless decay mechanisms. Despite the
wide information extracted from time-resolved experimental techniques
about lifetimes and energetics, structural details of the detected
intermediates are often unknown. Therefore, theoretical investigations
of reaction pathways and simulations of excited state dynamics and
decay play an important part in completing the picture. This work
presents recent methodological developments in semi-empirical
surface-hopping approaches and QM/MM embedding based on the DFTB and
OM2/MRCI methods. Prospects for application to biological systems as
well as limitations of the underlying QM methods are reviewed.