An overview of the CASVB approach to modern valence bond calculations

We discuss all of the key features of our current CASVB methodology for modem valence bond calculations on ground and excited states. The CASVB strategy may be used to generate compact representations of CASSCF wavefunctions or, alternatively, to perform the fully-variational optimization of various general types of VB wavefunction. We report also a new application, namely to the fourteen pi electrons of a planar dimethylenecyclobutadiene chain with three rings.