Electronic structure computations hybrid models

Explanations for the existence of hypervalent species started with Pauling s proposal of d orbital hybridization [3] where, for example, a set of sp d hybrid orbitals on sulfur was put forward to account for the hexavalence of SFg. Chemical computations [4] ruled out the participation of d atomic orbitals. A later model, the Rundle-Pimentel three-center, four-electron (3c-4e) bonding model [5], does not require d orbital participation and, so, is consistent with chemical computations. Other hypervalency models include the diabatic state model of Dixon and coworkers [6] and the democracy principle of Cooper and coworkers [7]. These various models provide useful insights into some aspects of the electronic structure of hypervalent molecules, but they don t provide an overarching description of these molecules that enables connections to be drawn between hypervalency and related molecular phenomena. 

What exactly are these surfaces First, they result from a full quantum mechanical calculation of the electronic structure of the molecule. Note that we do not use electronegativities or hybridizations or bond dipoles or any of the descriptive features of our bonding model in such calculations. These are a priori quantum mechanical calculations, and their output enables the charge distribution in a molecule to be computed. 

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