Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Theoretical Chemistry

Quantum Chemistry of Complex Molecular Systems

Complex molecular systems, such as mono- and polynuclear transition metal compounds, play a key role in many areas of chemistry. 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 describe 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 that enable the application of large active spaces. With the help of these methods it is possible to correctly describe complex molecules that are difficult if not impossible to access using conventional electronic structure methods. 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.

 

Method Development
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.[1] In this regard, our group was involved in the development of approaches to incorporate dynamic electron correlation as well as spin-orbit coupling to molecular DMRG calculations.[2,3] 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.[4] Furthermore, it features the unique ASS1ST scheme that allows for a chemically motivated and physically sound selection of active orbitals.[5,6] The MOLBLOCK Code will be made available here in due course.
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  • [1] A. Khedkar, M. Roemelt, Phys. Chem. Chem. Phys. 2021, 23, 17097-17112
  • [2] M. Roemelt, J. Chem. Phys. 2015, 143, 044112
  • [3] M. Roemelt, S. Guo, G. K.-L. Chan, J. Chem. Phys. 2016, 144, 204113
  • [4] M. Roemelt, V. Krewald, D. A. Pantazis, J. Chem. Theory. Comp. 2018, 14, 166-179
  • [5] A. Khedkar, M. Roemelt, J. Chem. Theory Comput. 2019, 15, 3522-3536
  • [6] A. Khedkar, M. Roemelt, J. Chem. Theory Comput. 2020, 16, 4993-5005

 

Transition Metal Chemistry and Spectroscopy
The accurate description and prediction of chemical and and spectroscopic properties of transition metal containing complexes remains in many cases a formidable challenge for quantum chemistry.[1] For example, the spin-state energetics of oligonuclear exchangecoupled transition-metal complexes are di cult to calculate quantitively and sometimes even qualitatively right.[2-4] Our group has devoted much e ort into studying transition metal chemistry using modern multireference methods as well other, more established methods.[ e.g. 5-7] A particular focus is here on open-shell systems and the multifaceted challenges they bring about.
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  • [1] A. Khedkar, M. Roemelt, Phys. Chem. Chem. Phys. 2021, 23, 17097-17112
  • [2] M. Roemelt, D. A. Pantazis, Adv. Theory Simul. 2019, 2, 1800201
  • [3] M. Roemelt, V. Krewald, D. A. Pantazis, J. Chem. Theory. Comp. 2018, 14, 166-179
  • [4] G. Singh, S. Gamboa, M. Orio, D. A. Pantazis, M. Roemelt, Theo. Chem. Acc. 2021, 140, 139
  • [5] A. Khedkar, M. Roemelt, Phys. Chem. Chem. Phys. 2020, 22, 17677-17686
  • [6] A. Berkefeld, M. Roemelt, C. Römelt, H. Schubert, G. Jeschke, Inorg. Chem. 2020, 59, 17234-17243
  • [7] E. B. Boydas, B. Winter, D. Batchelor, M. Roemelt, Int. J. Quant. Chem. 2020, e26515

 

Theoretical Organic and Organometallic Chemistry
In addition to studies of electronically complex transition metal systems (see here), our group has engaged in various projects that involve computational studies of the reactivity of different organic and organometallic systems using more traditional computational approaches based on density functional theory and coupled cluster methods.[1-2] For example, we have published multiple studies concerning the selective reduction of CO2 to more useful chemicals by homogeneous catalysts.[3-6]
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  • [1] O. Koleda, T. Broese, J. Noetzel, M. Roemelt, E. Suna, R. Francke, J. Org. Chem. 2017, 82, 11669-11681
  • [2] A. F. Roesel, M. Ugandi, N. T. T. Huyen, M. Majek, T. Broese, M. Roemelt, R. Francke, J. Org. Chem. 2020, 85, 8029-8044
  • [3] L. Iffland, A. Khedkar, A. Petuker, M. Lieb, F. Wittkamp, M. van Gastel, M. Roemelt, U.-P. Apfel, Organometallics 2019, 38, 289-299
  • [4] A. Rosas-Hernández, H. Junge, M. Beller, M. Roemelt, R. Francke, Cat. Sci. Technol. 2017, 7, 459-467
  • [5] R. Francke, B. Schille, M. Roemelt, Chem. Rev. 2018, 118, 4631-4701
  • [6] E. Oberem, A. F. Roesel, A. Rosas-Hernández, T. Kull, S. Fischer, A. Spannenberg, H. Junge, M. Beller, R. Ludwig, M. Roemelt, R. Francke, Organometallics 2019, 38, 1236-1247