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Ab initio methods for the theoretical description of catalytic oxidation reactions with molecular oxygen (Prof. Werner)

Calculation of reaction paths and characterization of reactive intermediates in catalytic oxidations (PD Rauhut, Prof. Stoll)

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Ab initio methods for the theoretical description of catalytic oxidation reactions with molecular oxygen

Project leader: Prof. Dr. H.-J. Werner

The aim of this project is the development and application of reliable ab initio methods for the investigation and characterization of intermediates, transition states and reaction pathways of catalytic oxidation reactions with molecular oxygen. The accuracy of these methods should surpass that of currently available DFT methods, in particular for open-shell multi-configuration problems (e.g. bi-radicalic intermediates). In the first funding period we will develop open-shell coupled-cluster methods with low-order (ideally linear) scaling of the computational resources with molecular size. These and other methods will be applied for the study of catalytically active copper and iron transition metal complexes and their interaction with substrates (alkanes, aromates). The effect of the environment (e.g. solvent, protein, zeolithes) will be investigated using QM/MM methods. The planned theoretical work will be carried out in close cooperation with the experimental projects C1 and C3. Furthermore, in cooperation with project B1 the mechanism of the cer-catalized hydroxylation of α-dicarbonyl compounds will be investigated. In the long term, local correlation methods will also be developed for multi-reference wavefunctions, in order to be able study bond-breaking situations and biradicalic species. These methods will also be applied to biologically relevant reactions, (e.g. P450 Cytochrom-P450 Monooxigenases). The aim is a detailed understanding of the mechanism of catalyzed oxidation reactions.

Published preliminary work

In recent years our group has developed local closed-shell electron correlation methods with linear scaling of the computational cost as function of the system size [1-3]. These new methods have made it possible to extend the applicability of high-level ab initio methods, such as local coupled cluster with single and double excitations and perturbative treatment of triple excitations (LCCSD(T)) to molecules with 50-100 atoms. Recently, the efficiency of these methods has been further improved using density fitting approximations [4-6]. For the optimization of molecular structures analytical energy gradients for local correlation methods [6] and multireference methods (MRPT2, CASPT2) [7] were also implemented. A QM/MM interface for local correlation methods was provided and tested for some enyzyme reactions [8]. In these calculations an unprecedented accuracy for activation enthalpies was achieved. In another study electron correlation effects in dicopper-oxygen complexes, which are model systems for enzymes like hemocyanine and tyrosinase, were investigated [9].

References

[1] M. Schütz, G. Hetzer, and H.­J. Werner, J. Chem. Phys. 111, 5691 (1999).
[2] M. Schütz and H.­J. Werner, Chem. Phys. Lett. 318, 370 (2000);
[3] M. Schütz and H.­J. Werner, J. Chem. Phys. 114, 661 (2001).
[4] H.­J. Werner, F. R. Manby, and P. J. Knowles, J. Chem. Phys., 118, 8149 (2003).
[5] R. Polly, H.­J. Werner, F. R. Manby, and P. J. Knowles, Mol. Phys., im Druck.
[6] M. Schütz, H.­J. Werner, R. Lindh, and F.R. Manby, J. Chem.Phys. 121, 737 (2004).
[7] P. Celani and H.­J. Werner, J. Chem. Phys. 119, 5044 (2003).
[8] R. da Mata, H.­J. Werner, S. Thiel and W. Thiel, Publikation in Vorbereitung.
[9] M. Rode and H.­J. Werner, Theor. Chem, Acc. 114, 309 (2005).

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Calculation of reaction paths and characterization of reactive intermediates in catalytic oxidations

Project leaders: PD Dr. G. Rauhut, Prof. Dr. H. Stoll

This project is intended to provide new theoretical insights into the elementary steps of catalytic reactions, such as the reaction of O₂ with aromatic compounds in zeolites (co-operation with project C1), or the reaction of n-alkanes to n-alkanoles with redox-active substrates in zeolites (co-operation with project A1). In order to achieve a reliable theoretical description of the above-mentioned processes, modern DFT methods will be used, and relativistic effects / spin-orbit coupling will be accounted for by effective core potentials (RECP). These methods will be improved, in the course of the project, both with respect to their accuracy and efficiency. We plan to introduce ab-initio correction terms into DFT in order to cope with the spin-coupling of open-shell systems, and to develop large-core RECPs and effective group potentials (EGPs) for an economic treatment of parts of the system not directly involved in the catalytic reaction. Characterization of adsorbates and reactive intermediates via harmonic IR spectra shall be supplemented by the calculation of selected anharmonic modes. New vibrational self-consistent field and configuration interaction (VSCF / VCI) methods shall be used (and further be developed) for this purpose.

References

[1] G. Rauhut, J. Chem. Phys. 2004, 121, 9313.
[2] G. Hübner, G. Rauhut, H. Stoll und E. Roduner, Phys. Chem. Chem. Phys. 2002, 4, 3112.
[3] G. Hübner, G. Rauhut, H. Stoll und E. Roduner, J. Phys. Chem. B 2003, 107, 8568.
[4] M. Dolg, U. Wedig, H. Stoll und H. Preuss, J. Chem. Phys. 1987, 86, 866.
[5] Datenbank: http://www.theochem.uni-stuttgart.de/pseudopotentials
[6] H. Stoll, B. Metz und M. Dolg, J. Comput. Chem. 2002, 23, 767.
[7] K.A. Peterson, D. Figgen, E. Goll, H. Stoll und M. Dolg, J. Chem. Phys. 2003, 119, 11113.
[8] D. Figgen, G. Rauhut, M. Dolg und H. Stoll, Chem. Phys. 2005, 311, 227.
[9] H. Stoll, Chem. Phys. Lett. 2003, 376, 141.
[10] G. Rauhut und H. Stoll, in preparation.
[11] G. Rauhut, in preparation.
[12] K. Pflüger, M. Paulus, S. Jagiella, T. Burkert und G. Rauhut, Theor. Chem. Acc. 2005, 114, 327.
[13] T. Leininger, A. Nicklass, W. Kuechle, H. Stoll, M. Dolg und A. Bergner, Chem. Phys. Lett. 1996, 255, 274.
[14] A. Nicklass und H. Stoll, Mol. Phys. 1995, 86, 317.