Development of Hybrid QM/QM Local Correlation Methods for the Study of Metal Sites in Biomolecular Catalysis

by Milica Andrejić
Doctoral thesis
Date of Examination:2015-03-27
Date of issue:2015-06-08
Advisor:Prof. Dr. Ricardo Mata
Referee:Prof. Dr. Ricardo Mata
Referee:Prof. Dr. Ulf Ryde
Referee:Prof. Dr. Guido Clever
Persistent Address: http://dx.doi.org/10.53846/goediss-5118

 

 

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Abstract

English

Metal-containing systems present a challenge for both theoretical and experimental chemists. Joint efforts are required to fully understand their complex electronic structure and their role in catalysis. On the side of theory, accuracy is essential but the cost of wave function methods is deterrent to this goal. The emphasis of this work is on the development of a QM/QM method for biomolecules which can reach wavefunction accuracy. To properly describe the electron correlation in transition metals inclusion of higher-order excitations is required. However, some of these effects are relatively local in nature (regularly connected with the metal center) and hybrid or embedding approaches offer a cost-effective alternative for their computation. In the proposed QM/QM scheme, localized orbitals are used to split the system into different groups. This allows for high accuracy in regions where bond breaking/formation takes place, while the remaining environment is described at a low level. Coupled cluster and MP2 approaches can be combined in a single calculation, without resource to model systems. In the present thesis, this QM/QM method will be applied for the first time in the treatment of closed-shell metal systems and for open-shell systems in general. The application on different complexes containing a wide variety of metals will be presented. It will be shown that this method provides valuable insights into the aurophilic interaction. On the example of molybdenum enzymes, it will be shown that high accuracy for the calculation of reaction pathways can be obtained with significantly reduced computational costs. On the example of nitrite reductase, it will also be shown that properties, such as electron affinities, can be reliably calculated.
Keywords: Local correlation methods; QM/QM method; Aurophilicity; Open shell systems; Molybdenum enzymes; Copper nitrite reductase
 
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