Local Hybrid QM/QM Calculations of Reaction Pathways in Metallobiosites

The accurate calculation of activation barriers is fundamental for the modeling of reaction pathways. However, the computational cost of describing electronic correlation at metal sites can be a deterrent. A possible solution to this problem is the use of hybrid QM/QM approaches, which combine different levels of theory in a single calculation. In this way, the metal and its direct vicinity can be treated, for example, with a coupled cluster method, with the remaining system at the MP2 level. We present calculations on two selected molybdenum complexes modeling the active sites of sulfite oxidase and dimethyl sulfoxide reductase. Use is made of the LMOMO scheme, a hybrid QM/QM model that enables the partition of the system directly at the orbital level, thus avoiding the use of model systems. The results show that even when the high-level calculations are restricted to the orbitals directly located at the metal atom, most of the electronic correlation effects are captured.