Our central field of research is Theoretical and Computational Chemistry, in particular Quantum Chemistry. We focus on theoretical developments that extend the scope of computational methodology, especially for large molecules, and we apply theoretical methods to study specific chemical problems, mostly in close cooperation with experimental partners. The activities of the group cover a broad methodological spectrum:
Recent applications from these areas address the rovibrational spectra of small molecules, catalytic reactions of transition metal compounds, excited-state dynamics, and enzymatic reactions. They thus range from accurate calculations on small molecules to the approximate modeling of very complex systems with thousands of atoms.
We compute vibration-rotation spectra of small molecules with high accuracy using correlated ab initio methods with large basis sets. In our past research in this area, coupled cluster CCSD(T) calculations were combined with second-order rovibrational perturbation theory to predict the spectroscopic constants of small reactive molecules, with sufficient accuracy to guide their spectroscopic identification and to assist in the analysis of their high-resolution vibration-rotation spectra. More recently, we have developed and implemented a general variational treatment of nuclear motion that allows the prediction of rovibrational energies and intensities not only for semirigid molecules, but also for molecules with large amplitude motion and for high rotational excitation. The variational calculations are based on accurate ab initio potential energy surfaces and dipole moment surfaces obtained at the coupled cluster level. Recent applications include the computation of complete rovibrational line lists for ammonia, the explanation of the unexpected intensity anomalies observed for oxadisulfane (HSOH), and purely theoretical predictions for thioformaldehyde with wavenumber accuracy. In the realm of electronic spectroscopy, we use high-level ab initio methods to provide theoretical benchmark data for the electronically excited states of representative organic chromophores.
We use density functional methods in studies of transition metal compounds to understand and predict their properties, with special emphasis on their electronic structure and catalytic reactivity. Much of the work on homogeneous catalysis involves a close collaboration with the experimental groups at our Institute and aims at a detailed mechanistic understanding of the reactions studied experimentally.
Such DFT applications include studies of:
* the mechanism of Ru-catalyzed olefin metathesis
* the stereochemistry of zirconocene-catalyzed olefin polymerization
* the activation of precatalysts in Pt- and Ru-catalyzed hydrosilylation
* the enantioselectivity of Rh-catalyzed hydrogenation
* the mechanism of Pd-catalyzed cross coupling reactions
* the origin of selectivity in Pd-catalyzed allylic alkylation reactions
* the electronic structure and spectra of iron-corrole complexes
* the electronic structure of carbon(0) and nitrogen(I) coordination compounds
DFT methods are also used as QM components in QM/MM investigations of enzymatic reactions.
This long-term project aims at the development of improved semiempirical quantum-chemical methods that can be employed to study ever larger molecules with useful accuracy. This includes the development of more efficient algorithms and computer programs. Applications are usually motivated by requests from experimental partners or by topical chemical problems, but they also serve to explore the limits of new methods and codes.
Methodological activities include:
In the past, we have applied semiempirical MNDO-type methods extensively to study the properties of fullerenes. Our emphasis has now shifted towards the investigation of the photochemistry of large organic chromophores at the OM2/GUGACI level using both static calculations and surface hopping simulations. Target systems include the nucleobases in the gas phase, in aqueous solution, and in DNA oligomers as well as fluorescent proteins, molecular motors, photochemical switches, and retinal models. In addition, semiempirical methods are used in QM/MM molecular dynamics simulations of enzymatic reactions.
This research focuses on hybrid approaches for large systems where the active center is treated by an appropriate quantum mechanical method, and the environment by a classical force field. It involves considerable method and code development. The QM/MM approach allows a specific modeling of complex systems such that most of the computational effort is spent on the chemically important part. Current applications primarily address biocatalysis and aim at a better understanding of enzymatic reactions including the role of the protein environment.
Methodological advances include:
While the QM/MM technology can be applied to many complex systems, we are most interested in enzymatic reactions. Recent investigations at different QM/MM levels address biocatalysis by heme enzymes (e.g., cytochrome P450), molybdopterin enzymes (e.g., xanthine oxidase), cystein proteases, fluorinases, lipases, chorismate mutase, p-hydroxybenzoate hydroxylase, and cyclohexanone monooxygenase. In addition, we also perform QM/MM studies on the spectroscopic properties of proteins, for examples on the Raman spectra of phycocyanin, the NMR spectra of vanadium-containing haloperoxidases, and the electronic spectra of fluorescent proteins. Surface hopping QM/MM simulations allow us to explore the excited-state dynamics of chromophores embedded in an environment.
Dr. Breidung, Jürgen
Dr. Cui, Ganglong
Dr. Dral, Pavlo
Escorcia Cabrera, Andrés Mauricio
Dr. Escudero Masa, Daniel
Dr. Fazzi, Daniele
Dr. Gámez Martinez, José Antonio
Dr. Götze, Jan
Dr. Ganguly, Abir
Dr. Gao, Xing
Dr. Gopinadhanpillai, Gopakumar
Dr. Korth, Martin
Dr. Koslowski, Axel
Dr. Lan, Zhenggang
Dr. Liao, Rong-Zhen
Prof. Dr. Lin, Hai
Dr. Patil, Mahendra
Dr. Ramos da Silva jun., Mario
Dr. Saito, Toru
Dr. Sen, Kakali
Spörkel, Lasse Jona
Prof. Dr. Thiel, Walter
Dr. Tuna, Deniz
van Rijn, Jeaphianne
Dr. Weingart, Oliver
Dr. Wolf, Lawrence
Dr. Wu, Xin
Dr. Yachmenev, Andrey
Dr. Zheng, Yiying
Arbeitsgemeinschaft Theoretische Chemie
Computional Chemistry List
Gesellschaft Deutscher Chemiker
International Academy of Quantum Molecular Sciences
World Association of Theoretical and Computational Chemists
RUB Solvation Science