MOLPRO

39 THE VB PROGRAM CASVB 288
This keyword is short-hand for strong orthogonality. The only allowed non-zero overlaps are
between pairs of orbitals (2n−1, 2n).
FULL;
This keyword is short-hand for full orthogonality. This is mainly likely to be useful for testing
purposes.
39.11 Wavefunction analysis
39.11.1 Spin correlation analysis
(NO)SCORR;
With this option, expectation values of the spin operators (ŝ µ +ŝ ν ) 2 are evaluated for all pairs of
µ and ν. Default is NOSCORR. The procedure is described by: G. Raos, J. Gerratt, D. L. Cooper
and M. Raimondi, Chem. Phys. 186, 233–250 (1994); ibid, 251–273 (1994); D. L. Cooper,
R. Ponec, T. Thorsteinsson and G. Raos, Int. J. Quant. Chem. 57, 501–518 (1996).
At present this analysis is only implemented for spin-coupled wavefunctions.
39.11.2 Printing weights of the valence bond structures
For further details regarding the calculation of weights in CASVB, see T. Thorsteinsson and
D. L. Cooper, J. Math. Chem. 23, 105-26 (1998).
VBWEIGHTS,key1,key2,. . .
Calculates and outputs weights of the structures in the valence bond wavefunction Ψ V B . key
specifies the definition of nonorthogonal weights to be used, and can be one of:
CHIRGWIN
LOWDIN
INVERSE
ALL
NONE
Evaluates Chirgwin-Coulson weights (see: B. H. Chirgwin and C. A. Coulson,
Proc. Roy. Soc. Lond. A201, 196 (1950)).
Performs a symmetric orthogonalization of the structures and outputs
the corresponding weights.
Outputs “inverse overlap populations” as in G. A. Gallup and J. M. Norbeck,
Chem. Phys. Lett. 21, 495–500 (1973).
All of the above.
Suspends calculation of structure weights.
The commands LOWDIN and INVERSE require the overlap matrix between valence bond structures,
and some computational overhead is thus involved.
39.11.3 Printing weights of the CASSCF wavefunction in the VB basis
For further details regarding the calculation of weights in CASVB, see T. Thorsteinsson and
D. L. Cooper, J. Math. Chem. 23, 105-26 (1998).
CIWEIGHTS,key1,key2,. . . [,N conf ];
Prints weights of the CASSCF wavefunction transformed to the basis of nonorthogonal VB
structures. For the key options see VBWEIGHTS above. Note that the evaluation of inverse overlap
weights involves an extensive computational overhead for large active spaces. Weights are