MOLPRO

39 THE VB PROGRAM CASVB 280
39 THE VB PROGRAM CASVB
CASVB is a general program for valence bond calculations
written by T. Thorsteinsson and D. L. Cooper (1996–2005).
This program can be used in two basic modes:
a) variational optimization of quite general types of nonorthogonal MCSCF or modern valence
bond wavefunctions
b) representation of CASSCF wavefunctions in modern valence form, using overlap- (relatively
inexpensive) or energy-based criteria.
Bibliography:
T. Thorsteinsson, D. L. Cooper, J. Gerratt, P. B. Karadakov and M. Raimondi, Theor. Chim.
Acta 93, 343–66 (1996).
D. L. Cooper, T. Thorsteinsson and J. Gerratt, Int. J. Quant. Chem. 65, 439–51 (1997).
D. L. Cooper, T. Thorsteinsson and J. Gerratt, Adv. Quant. Chem. 32, 51–67 (1998).
T. Thorsteinsson and D. L. Cooper, in Quantum Systems in Chemistry and Physics. Volume 1:
Basic problems and models systems, eds. A. Hernández-Laguna, J. Maruani, R. McWeeny, and
S. Wilson (Kluwer, Dordrecht, 2000); pp 303–26.
All publications resulting from use of this program should acknowledge relevant publications.
There is a more complete bibliography at http://www.liv.ac.uk/ dlc/CASVB.html
39.1 Structure of the input
All CASVB sub-commands may be abbreviated by four letters. The general input structure can
be summarized as follows:
a) For generating representations of CASSCF wavefunctions, the program is invoked by the
command CASVB. For variational optimization of wavefunctions it is normally invoked
inside MULTI by the sub-command VB (see 19.10).
b) Definition of the CASSCF wavefunction (not generally required).
c) Definition of the valence bond wavefunction.
d) Recovery and/or storage of orbitals and vectors.
e) Manual input of starting guess (optional).
g) Optimization control.
f) Definition of molecular symmetry and possible constraints on the VB wavefunction.
h) Wavefunction analysis.
i) Further general options.
Items a) and b) should precede everything else in the input; apart from this, commands may
come in any order.