Multi-level extensions of the local correlation cluster-in-molecule (CIM) framework, which enable one to combine different quantum chemistry methods to treat different regions in large molecular systems, will be discussed. Multi-level CIM schemes that are particularly useful combine higher-level ab initio methods, including coupled-cluster (CC) approaches that can handle reaction pathways characterized by significant bond rearrangements, such as CR-CC(2,3), which can be used to treat the reactive part of a large system, with lower-order local or (if affordable) canonical methods, such as MP2 or CCSD, to describe chemically inactive regions. Illustrative applications will include the proton transfer reactions in the aggregates of dithiophosphinic acids with the water molecules and the Co-C bond dissociation in methylcobalamin, where the second-order multi-reference perturbation theory as well as the hybrid density functional theory (DFT) methods, particularly those with a significant fraction of the Hartree-Fock exchange, and the DFT approaches without dispersion corrections face considerable challenges.

Multilevel extensions of the cluster-in-molecule local correlation methodology aimed at chemical reaction pathways involving large molecular systems

244th National Meeting (2012)

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