Computational Methods for Organotin Compounds

Sarah R. Whittleton, Russell J. Boyd, and T. Bruce Grindley Department of Chemistry, Dalhousie University, Halifax, Canada B3H4J3 

The primary focus of computational chemistry is to employ theoretical methods to solve problems related to chemical systems. An important part of computational chemistry involves choosing the most appropriate method/ based on the type of chemical system and the chemical properties of interest. Because there are an endless number of methods available, choosing computational methods for organotin systems epitomizes this dilemma. 

The radial expansion of valence orbitals introduces substantial alterations in the chemical bonding and valence spectroscopic properties of heavy-element systems. Therefore to perform computational calculations on heavy elements such as tin, it is mandatory to include relativistic effects to determine electronic structure and to ensure quantitative agreement with experimental data.  

Accounting for relativistic effects in computational organotin studies becomes complicated, because Hartree-Fock (HF), density functional theory (DFT), and post-HF methods such as n-th order Mpller-Plesset perturbation (MPn), coupled cluster (CC), and quadratic configuration interaction (QCI) methods are non-relativistic. Relativistic effects can be incorporated in quantum chemical methods with Dirac-Hartree-Fock theory, which is based on the four-component Dirac equation. Unformnately the four-component Flamiltonian in the all-electron relativistic Dirac-Fock method makes calculations time consuming, with calculations becoming 100 times more expensive. The four-component Dirac equation can be approximated by a two-component form, as seen in the Douglas-Kroll (DK) Hamiltonian or by the zero-order regular approximation To address the electron cor- 

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