Dr. Michael Römelt
Lehrstuhl für Theoretische Chemie
Phone: +49 (0)234 32 26749
Complex molecular systems, such as mono- and polynuclear transition metal compounds, play a key role in many areas of chemistry. They serve a multitude of purposes in various applications in homogeneous inorganic and bioinorganic catalysis as well as functional materials. Yet understanding and predicting their properties as well as their reactivity is a great challenge and one of the current frontiers of theoretical chemistry. Our research group focuses on both, the development of novel quantum chemical methods that are especially designed to tackle complex molecules and on the application of existing methods to tackle interesting chemical problems. The former aspect of our work is centered around modern multireference methods such as the density matrix renormalization group. With the help of these methods it is possible to correctly describe complex molecules that are difficult if not impossible to access using conventional methods like the complete active space self-consistent field (CASSCF). In addition to our efforts in theory development we conduct computational studies of different inorganic and organic systems using a variety of quantum chemical methods, ranging from density functional theory to high-level ab initio multireference methods. These studies concern chemical reactivities as well as spectroscopic properties. A short description of a selection of our research projects can be found below while the full list of publications can be viewed here.
We have open PhD positions! If you are interested in joining our team, please contact us via firstname.lastname@example.org
In recent years, considerable progress was made in the field of multireference methods. In particular, the emergence of methods like the DMRG, Full-CI Quantum Monte-Carlo and various selective CI methods has opened up new perspectives and possibilities. In this regard, our group was involved in the development of approaches to incorporate dynamic electron correlation as well as spi n-orbit coupling to molecular DMRG calculations. Nevertheless, molecules with many strongly correlated electrons still pose a formidable challenge to electronic structure methods, partially owing to methodological gaps. Therefore, we have developed our own MOLBLOCK code that is dedicated to this particular kind of problem setting. Pilot studies show that it can be used to perform large-scale multireference studies on chemically relevant systems with high accuracy. Furthermore, it features the unique ASS1ST scheme that allows for a chemically motivated and physically sound selection of active orbitals. The MOLBLOCK Code will be made available here in due course.
- A. Khedkar, M. Roemelt J. Chem. Theory Comput. 2020, https://doi.org/10.1021/acs.jctc.0c00332
- A. Khedkar, M. Roemelt J. Chem. Theory Comput. 2019, 15, 3522-3536
- M. Roemelt, S. Guo, G. K.-L. Chan J. Chem. Phys. 2016, 144, 204113
- M. Roemelt J. Chem. Phys. 2015, 143, 044112
- M. Roemelt, V. Krewald, D. A. Pantazis J. Chem. Theory. Comp. 2018, 14, 166-179
Magnetic Properties of Transition Metal Compounds
The accurate description and prediction of magnetic properties of transition metal containing complexes remains in many cases a formidable challenge for quantum chemistry. In particular, the spin-state energetics of oligonuclear exchange-coupled transition-metal complexes are difficult to calculate quantitively and sometimes even qualitatively right. Our group is involved in multiple studies of magnetic properties using modern multireference methods. For example, in a recent pilot study of a biomimetic mixed-valence Mn dimer we were able the first to calculate the exchange coupling constant of a realistically sized molecule with more than two unpaired electrons by means of wavefunction based ab initio electronic structure methods.
- M. Roemelt, V. Krewald, D. Pantazis J. Chem. Theory Comput. 2018, 14, 166-179
- M. Roemelt, D. A. Pantazis Adv. Theory. Simul. 2019, 2, 1800201
- A. Sharma, M. Roemelt, M. Reithofer, R. R. Schrock, B. M. Hoffman, F. Neese Inorg. Chem. 2017, 56, 6906-6919
Fe-Mediated Cross-Coupling Reactions
Organoferrates(III) of the composition [FeR3R′]- have previously been identified in multiple studies as reaction intermediates during Fe-mediated cross coupling reactions. They are readily formed under reaction conditions and are able to efficiently eliminate cross coupling products which is a key step of the total reaction. In a recent work we were able to provide a detailed picture about the reaction mechanism that explains the experimentally observed chemoselectivity in the gas-phase for a set of eight organoferrates(III) with composition [Ph3FeR]- by means of large-scale multireference calculations. An interesting aspect of the proposed mechanism is the central role of the total spin which changes in the course of the reaction and governs the type of reaction mechanism.
- M. Khedkar, M. Roemelt Phys. Chem. Chem. Phys. 2020, DOI: 10.1039/D0CP02834G
Selective Reduction of CO2
The selective reduction of CO2 to chemically valuable products like CO and formic acid is of high scientific, economic and social importance. In recent years we have engaged in multiple studies of molecular catalysts that are able to selectively transform CO2 into one of the aforementioned products. During those studies, our theoretical calculations were accompanied by investigations with various chemical, electrochemical and spectroscopic techniques. Eventually, the combined theoretical and experimental efforts resulted in coherent pictures about the remarkable chemical properties of the investigated systems.
- L. Iffland, A. Khedkar, A. Petuker, M. Lieb, F. Wittkamp, M. van-Gastel, M. Roemelt, U.-P. Apfel Organometallics 2019, 38, 289-299
- E. Oberem, A. Rösel, A. Rosas-Hernández, T. Kull, S. Fischer, A. Spannenberg, H. Junge, M. Beller, R. Ludwig, M. Roemelt, and R. Francke Organometallics 2019, 38, 1236-1247
- R. Francke, B. Schille, M. Roemelt Chem. Rev. 2018, 118, 4631-4701
- A. Rosas-Hernández, H. Junge, M. Beller, M. Roemelt, R. Francke Cat. Sci. Technol. 2017, 7, 459-467