Ab initio photochemistry of complex systems:
Photochemical reactions
of large molecules, in particular in
solution, can be studied using our recently developed
nonadiabatic ab initio molecular dynamics method (na-AIMD)
taking into account all nuclear degrees of freedom.
- Applications:
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The
photoisomerisation of azobenzene derivatives
plays an important role in materials science for the
development of optical storage media, optical switches, and
light-powered nanomachines.
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Knowledge of the photophysical properties of DNA bases and base pairs is the key to understanding the mechanisms
leading to radiation induced genetic damage.
Changes in the molecular structure following photoexcitation
as well as the route for subsequent
radiationless decay can provide important clues.
Method development:
- Extension of na-AIMD to multiple electronic states using
TDDFT. An ongoing collaboration with Prof. Kosov (Maryland)
on the development of analytical gradients for
TDDFT excited states as well as nonadiabatic
coupling elements has existed for several years.
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Molecular aggregation through hydrogen bonding:
Within the DFG funded
Research Collaboration FOR 618 "Aggregation
of small molecules" we study amino acids in aqueous solution
using AIMD. Apart from conformational changes we
investigate the neutral-zwitterionic transition as a
function of the degree of solvation. Furthermore, we plan to
use AIMD to study the co-crystallization in formamide-water
mixtures. Our calculations are accompanied by the
experimental efforts of Prof. Kleinermanns (Düsseldorf),
Profs. Sander and Havenith (Bochum) and Prof. Boese (Essen).
Diffusion and speciation of dissolved oxides in
H2O at high pressures and temperatures:
This project is carried out in collaboration with
Prof. Maresch (Institut für Geologie, Mineralogie und
Geophysik, Bochum) within the
Collaborative Research Centre (SFB) 526
"Rheology of the Earth - from the Upper Crust to the
Subduction Zone". Speciation and diffusion of quartz and
other minerals in water at high
temperatures and pressures will be investigated
theoretically by means of
AIMD simulations as well as
experimentally using Raman spectroscopy and Fabry-Perot
interferometry.
Diffusion processes at solid-solid-liquid
interfaces:
This project is carried out in collaboration with
Prof. Renner (Institut für
Geologie, Mineralogie und Geophysik, Bochum)
within the
Collaborative Research Centre (SFB) 526
"Rheology of the Earth - from the Upper Crust to the
Subduction Zone". Diffusion processes and surface reactions
potentially leading to groove formation at the quartz-water interface
will be studied using AIMD and AFM measurements.
Novel constraint methods for free energy and rare events:
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Applications: Study of tautomerisation of
DNA bases and base pairs in ground and excited state, in
particular in aqueous solution using
coordination constraints. Goal: Understanding of genetic
damage caused by the formation of so-called rare tautomers.
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Method development:
Development and implementation of novel constraint methods
within the framework of AIMD. The aim is to search for low
energy reaction paths on complex free energy landscapes and
to be able to reconstruct the latter at least partially.
Our recent developments along these lines include
the Dynamic Distance method and Targeted
AIMD. Going beyond a purely ab initio implementation we plan to
extend the applicabilty of these methods to large
biochemical systems by using a hybrid quantum-classical
QM/MM approach. This work has been carried out
in collaboration with Dr. Markwick (Grenoble),
Prof. Marx (Bochum) and Prof. Schlitter (Bochum).
Developments within the CPMD package:
-
nonadiabatic dynamics (ab initio surface hopping,
QM/MM extension)
- new geometric constraints (Targeted MD, Dynamic
Distance Constraint)
- time-dependent density functional theory (TDDFT
excitation energies, gradients, and nonadiabatic couplings)
- new density functionals (HCTH family)
