Ab Initio Modern Valence Bond Theory

We concentrate in the present account on certain recent developments linked to extensions of spin-coupled theory. In particular, we describe the so-called SCVB* strategy, which employs optimised virtual orbitals to reduce still further the number of nonorthogonal configurations required in accurate calculations of ground and excited state potential energy surfaces. We also outline the CASVB approach, which may be used to generate modern valence bond representations of complete active space self-consistent field wavefunctions or, alternatively, to perform the fully-variational optimisation of quite general types of single- and multicon-figuration modern VB wavefunctions for ground and excited states.

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