Theory of hybrid Quantum Mechanical Molecular Mechanical methods. An introduction to a way of treating complex chemical systems.

Abstract

A combined Quantum Mechanical (QM) and Molecular Mechanical (MM) method QM/MM seems a promising way to treat complex chemical systems. Rooted in the basic articles by Singh, & Kollman [Singh and Kollman, 1986] and Field, Bash, & Karplus [Field et al., 1990] we will introduce ourselves to the ideas and theory behind the QM/MM method. We will among other stuff discuss the following items.

• Reasonable criteria for partitioning a molecular system in a QM part and a MM part.
• Problems associated with broken bonds in partitioning a molecular system (introduction of link atoms).
• The look of the total hamilton operator describing the system with special emphasis on the interaction operator between the QM part and the MM part.
• Behaviour of the model in comparison to pure gas phase quantum mechanical calculations as well as molecular statistical calculations (the Cl^- plus CH₃Cl reaction).

The subject of the talk might be of interest to people dealing with both small organic systems in solution as well as to people trying to model large enzyme systems.

Additional suggested reading

• [Singh and Kollman, 1986]
• [Field et al., 1990]
• [Eurenius et al., 1996] : More recent review article concerning QM/MM with methods for reaction path determination.
• [Gao, 1996] : More recent review article concerning QM/MM with critical evaluation of the method.
• [Weiner et al., 1985] : Application of QM/MM to a model system describing amide hydrolysis in aqueous solution.
• [Weiner et al., 1986] : Application of QM/MM to amide hydrolysis catalysed by a serine protease enzyme.

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