Summary of key facilities in CASVB

The program can be used in two basic modes:

To generate representations of CASSCF wavefunctions in modern valence form, using an overlap-based criterion (relatively inexpensive) or an energy-based criterion;
To carry out fully-variational optimization of quite general types of nonorthogonal MCSCF or modern valence bond wavefunctions.

CASVB can handle any allowed spin state and offers a choice of spin basis (Rumer, Kotani, 'projected', and so on). There are various optional facilities to deal with point group symmetry and/or constraints. As well as treating the lowest state of a given symmetry, the program can be used to perform calculations for n^th-order saddle points. Properties (including gradients but not second derivatives) are available in the same way as for other types of MCSCF wavefunction. Further CASVB facilities are described in the manual.

The SPINS program also provides a means of transforming between different spin bases.