Multiconfiguration Valence Bond Methods with Optimized Orbitals

5 Multiconfiguration Valence Bond Methods with Optimized Orbitals 

The Valence Bond Self-Consistent Field (VBSCF) method has been devised by Balint-Kurti and van Lenthe (32), and was further modified by Verbeek (6,33) who also developed an efficient implementation in a package called TURTLE (11). Basically, the VBSCF method is a multiconfiguration SCF procedure that allows the use of nonorthogonal orbitals of any type. The wave function is given as a linear combination of VB structures, (Eq. 9.7). 

The VBSCF method permits complete flexibility in the definition of the orbitals used for constructing the VB structures, d A-. The orbitals can be allowed to delocalize freely during the orbital optimization (resulting in 

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