Generalized valence bond perfect pairing

Amovilli et al. [20] presented a method to carry out VB analysis of complete active space-self consistent field wave functions in aqueous solution by using the DPCM approach [3], A Generalized Valence Bond perfect pairing (GVB-PP) level... 

Generalized valence bond perfect pairing (GVB/PP) and spin-coupled valence bond (SCVB) calculations for tri- and polyatomic molecules use multicentre, delocalized orbitals (i.e. 3-centre or many-centre orbitals) to accommodate the active space electrons. To quote Ref 27 The GVB/PP wavefimctions are antisymmetrized products of paired orbitals and represent a single valence bond structure.. .. The SC method is based on a single configuration in which each electron is described by a distinct orbital. The complete spin state is utilized. For example, a 4-electron 3-centre SC wavefunction involves four non-orthogonal 3-centre or-... 

The generalized valence bond (GVB) method was the earliest important generalization of the Coulson—Fischer idea to polyatomic molecules (13,14). The method uses OEOs that are free to delocalize over the whole molecule during orbital optimization. Despite its general formulation, the GVB method is usually used in its restricted form, referred to as GVB SOPP, which introduces two simplifications. The first one is the perfect-pairing (PP) approximation, in which only one VB structure is generated in the calculation. The wave function may then be expressed in the simple form of Equation 9.1, as a product of so-called geminal two-electron functions ... 

GVB Generalized valence bond. A theory that employs CF orbitals to calculate electronic structure with wave functions in which the electrons are formally coupled in a covalent manner. The simplest level of the theory is GVB PP (PP-perfect pairing), in which all the electrons are paired into bonds, as in the Lewis structure of the molecule. 

Fig. 6. Average relativistic effective core potential and relativistic effective core potential energy curves for two states of Bi2. HF, Hartree-Fock GVB(pp), eight-configuration perfect-pairing generalized valence bond FVCI, full-valence Cl based on the GVB(pp) wave functions FV7R, full-valence Cl plus single and double promotions to virtual MOs relative to seven-dominant configurations. (The FVCI and FV7R calculations include the REP-based spin-orbit operator.)...

In order to gain both a more local and a more accurate description of the bonding in SF we introduced intra-pair correlations via the perfect pairing generalized valence bond method (GVB-PP) (35). The valence electrons are described by generalized Heitler-London pairs,... 

The approximate bonding energy of the four valence electrons in HgCl2 may be written down by applying Mulliken s general formula 124), based on the valence-bond approximation of perfect pairing. Representing the structure Cl—Hg —Cl in the manner... 

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