Lehrstuhl für Theoretische Chemie 

Welcome to the Marx Group!Scientific Interests of the Marx Group: A Short Overview
The general theme of our research consists in understanding structure,
dynamics, and chemical reactions of
complex molecular manybody systems  bridging the gap between
chemistry and physics. Our aim is to capture nature as closely
as possible by theoretical means  the basic entities being nuclei
and electrons. This implies that we have to use
atomistic ab initio computer simulation techniques
which are capable of including dynamics and quantum mechanics 
of course only approximatively. The notion "ab initio" or
"first principles" means for us that we neither want to fit
to experimental data nor do we want to adjust any parameters.
The central working horse to turn these ideas into practical numerical tools
are in particular the ab initio simulation methods going
back to ideas of Car and Parrinello (1985).
The crucial idea of the CarParrinello approach to ab initio molecular dynamics consists in efficiently solving the electronic structure problem "on the fly" as the molecular dynamics trajectory is generated for a set of classical nuclei using Newtonian mechanics. Thus, within ab initio simulations it is neither required to compute a highdimensional global potential energy surface prior to the simulation, nor is it necessary to reconstruct it approximately from local pair (or fewbody) interactions. This "classical" CarParrinello approach has been extended by Marx and Parrinello (1994) to include also the nuclei as quantummechanical degrees of freedom. In order to achieve this for "large systems" composed of the order of 100 nuclei or more, the FeynmanKac formulation of quantum statistical mechanics in terms of path integrals is employed. This class of fully quantummechanical ab initio path integral techniques makes it possible to study  in a timeaveraged sense  zeropoint motion and tunneling effects for instance of protons in hydrogenbonded or other complex environments. More recently, another extension of the original CarParrinello method, which assumed the electrons to stay in the electronic ground state, was developed by Doltsinis and Marx (2002). The basic idea of this nonadiabatic ab initio dynamics technique is to use Tully's surface hopping algorithm in combination with the socalled restricted openshell KohnSham Ansatz. This efficient approach "beyond the BornOppenheimer approximation" allows us to study photochemical reactions with particular focus on laserinduced processes in solution. We have developed a multideterminant CarParrinello propagation scheme, which enables the description of the dynamics of electronic states that cannot be represented using a single KohnSham determinant. Using this strategy, we have computed Heisenberg's antiferromagnetic exchange coupling obtained from a spinprojected, Hubbardcorrected, brokensymmetry ground state. Generating the time evolution of this quantity "on the fly" provides access to magnetostructural dynamics, which arise from the intricate coupling of molecular motion and magnetic properties. A field pioneered in Bochum is the general theory and computer simulation of covalent mechanochemistry. In contrast to thermochemistry, photochemistry or electrochemistry (where temperature, light or electricity are used to trigger reactions), mechanochemistry utilises mechanical force to activate and control chemical reactions. Advances in this field impact on areas of application currently under investigation such as molecular nanomechanics of singlemolecule junctions, functionalized surface coatings, and mechanoenzymes. Among the most recent developments is a method that allows us to solvate molecular complexes in superfluid helium droplets at subKelvin temperatures. It combines ab initio path integrals to treat chemically complex molecular solutes with a Monte Carlo sampling of the helium environment, in order to establish quantum mechanical indistinguishability  as required by the BoseEinstein quantum statistics of liquid ^{4}He. This approach opens the doorway to the study of chemical reactivity in the absence of thermal energy, such as aggregationinduced dissociation phenomena and cryochemical reactions. The evergrowing family of ab initio simulation techniques is ideally suited to the investigation of disordered systems at finite temperatures; molecular liquids being a prime example of this. As such, this set of methods provides the most direct insight into the structure and dynamics of solvation shells, the impact of hydrogen bonding on the properties of aqueous solutions, and, most importantly, the influence of solvation on chemical reactivity. These simulation algorithms together with the required computer hardware constitute what we like to call a "Virtual Laboratory". In this theoretician's version of a real laboratory chemical reactions of molecules can take place at finite temperature in liquids or on surfaces  solely governed by the basic laws of physics. This makes it possible to investigate "chemically complex" molecular systems  possibly in close contact with experimentalists. To foster this, the Marx Group is or has been involved in several largescale collaborative research projects such as SFB 558 ("Heterogeneous Catalysis"), FOR 436 ("Water at Interfaces"), FOR 618 ("Molecular Aggregation") and various Projects of the VolkswagenStiftung ("StressControlled Molecular Electronics", "Multiscale Modelling"). In particular, key research of the Marx Group is carried out in the framework of the Research Department "Interfacial Systems Chemistry" ( RD IFSC ) and the Research Consortium " Solvation Science@RUB " supplemented by the Koselleck Focus Group on " Covalent Mechanochemistry and Molecular Nanomechanics ".
Much more detail on this topic can be found in the monograph
The research group itself consists (as a time average) of physicists, chemists, and biochemists and it is characterized by transdisciplinarity. The spectral range of our interests is rather broad and covers applications to molecules, clusters, liquids, solids, surfaces, as well as to biologically relevant species. In order to be able to achieve these goals, we are constantly developing novel techniques and/or we are improving existing methods. Some of our current and recent projects are:
 Trotter Discretization Errors: Simple "A Priori" Estimates  Ab initio path integral Monte Carlo simulations  Bosonic Exchange: Superfluid Helium  Quantum Fluctuation Effects on Photoabsorption Spectra  Scrutinizing Centroid and Ring Polymer Path Integral Molecular Dynamics  Quantum Effects on Vibrational and Electronic Spectra of Hydrazine
If you want to know more about the various ab initio simulation
techniques used and developed in the Marx group
and applications of these methods we recommend to have a
look at our local
collection of books and review articles on the subject.
The
publication lists of Dominik Marx and the Marx Group
can be obtained as a pdf file (CV of Professor Marx).
Note that it is illegal to download most of the articles listed there: please
contact us at
theochem@theochem.rub.de and you will receive legal reprints as soon as possible.


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