A Valence Bond Method with Polarizable Continuum Model

The BLW method can be considered as an extension of the orbital deletion procedure (ODP) (51,52), a simpler method that can only be applied to carbocations (52) and boranes (51). The ODP consists of representing a resonance structure displaying an electronic vacancy (Lewis acid character) by deleting the primitive basis functions corresponding to the empty site before launching the SCF calculation. As a typical example, the ODP has been applied to calculate the resonance energy of the allyl cation (52). 

5 A VALENCE BOND METHOD WITH POLARIZABLE CONTINUUM MODEL 

The valence bond method with polarizable continuum model (VBPCM) method (55) includes solute—solvent interactions in the VB calculations. It uses the same continuum solvation model as the standard PCM model implemented in current ab initio quantum chemistry packages, where the solvent is represented as a homogeneous medium, characterized by a dielectric constant, and is polarizable by the charge distribution of the solute. The interaction between the solute charges and the polarized electric field of the solvent is taken into account through an interaction potential that is embedded in the 

Hamiltonian and determined by a self-consistent reaction field (SCRF) procedure. 

In its actual implementation, the VBPCM method is based on the VBSCF method (see above). Thus, the wave function is expressed in the usual manner as a linear combination of VB structures, Equation 9.8, but now these VB structures are optimized and interacting with one another in the presence of a polarizing field of the solvent, by a self-consistent procedure. Within this model, the interaction between solute and solvent is represented by an interaction potential, VR, which is treated as a perturbation to the Hamiltonian H° of the solute molecule in vacuum. The Schrodinger equation for the VB wave function now reads 

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