Valence Bond Self-Consistent Field Method with Localized Orbitals

1 Valence Bond Self-Consistent Field Method with Localized Orbitals 

The flexibility of the valence bond self-consistent field (VBSCF) method can be exploited to calculate VB wave functions based on orbitals that are purely localized on a single atom or fragment. In such a case, the VBSCF wave function takes a classical VB form, which has the advantage of giving a very detailed description of an electronic system, as, for example, the interplay between the various covalent and ionic structures in a reaction. On the other hand, since covalent and ionic structures have to be explicitly considered for 

Consider, for example, the dissociation of an A-B bond, where A and B are two polyelectronic fragments. Including the two HAOs that are involved in the bond in the active space, and the adjacent orbitals and electrons in the spectator space, the VBSCF wave function reads as follows  

For a typical elementary reaction, such as SN2, consisting, for example, of the breaking of a C F bond followed by the formation of a new C Cl bond (Eq. 9.9), 

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VBSCF Valence bond self-consistent field. A VB computational method. The VBSCF wave function is a linear combination of VB structures that simultaneously optimizes the structural coefficients and the orbitals of the structures. It can be used with any type of AOs OEOs, BDOs, and HAOs. With HAOs, we refer to the method as L-VBSCF L = localized. 

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