MOLPRO

39 THE VB PROGRAM CASVB 284
be projected onto the present active space (note that it is necessary to specify a record name for
the molecular orbitals (orb in the START commmand) for this to be possible).
Default for record is the vb record name specified in keyword START (if applicable).
39.8 Permuting orbitals
ORBPERM,i 1 ,. . . ,i mact ;
Permutes the orbitals in the valence bond wavefunction and changes their phases according
to φ ′ j = sign(i j)φ abs(i j ). The guess may be further modified using the GUESS keyword. Also
the structure coefficients will be transformed according to the given permutation (note that the
configuration list must be closed under the orbital permutation for this to be possible).
39.9 Optimization control
39.9.1 Optimization criterion
CRIT,method;
Specifies the criterion for the optimization. method can be OVERLAP or ENERGY (OVERLAP
is default). The former maximizes the normalized overlap with the CASSCF wavefunction:
( )
〈ΨCAS |Ψ V B 〉
max
(〈Ψ V B |Ψ V B 〉) 1/2
and the latter simply minimizes the energy:
min
( )
〈ΨV B |Ĥ|Ψ V B 〉
.
〈Ψ V B |Ψ V B 〉
39.9.2 Number of iterations
MAXITER,N iter ;
Specifies the maximum number of iterations in the second order optimizations.
N iter =50.
Default is
39.9.3 CASSCF-projected structure coefficients
(NO)CASPROJ;
With this keyword the structure coefficients are picked from the transformed CASSCF CI vector,
leaving only the orbital variational parameters. For further details see the bibliography. This
option may be useful to aid convergence.
39.9.4 Saddle-point optimization
SADDLE,n;
Defines optimization onto an n th -order saddle point. See also T. Thorsteinsson and D. L. Cooper,
Int. J. Quant. Chem. 70, 637–50 (1998).