MR-SCVB

The right-hand panel of Figure 1 compares the excited curve obtained from the final MR-SCVB (or, MRVB for short) calculation with that from the full Cl. In this study, starting with the double-reference SC functions, we optimized a set of 4 pairs of virtuals for each reference and, at the end, we built a VB wavefunction consisting of 84 spatial configurations for a total of only 125 VB structures. This... 

Finally, we mention preliminary results of MR-SCVB calculations for full potential energy surfaces of LiH. The ground-state surface describes adiabatically the reaction... 

The ab initio spin-coupled valence bond (SCVB) approach continues to provide accurate ground and excited state potential energy surfaces for use in a variety of subsequent applications, with particular emphasis on intermolecular forces and reactive systems. The compactness of the various wavefunctions allows direct and clear interpretation of the correlated electronic structure of molecular systems. Recent developments, in the form of SCVB and MR-SCVB, involve the optimization of virtual orbitals via an approximate energy expression. These improved virtuals lead to still higher accuracy for the final variational wavefunctions, but with even more compact wavefunctions. 

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