32.4.1 Specifying orbital configurations

The number of core and active orbitals ($mcore$, $mact$), active electrons ($Nact$), and the value of the total spin will be identical to that defined for the CASSCF wavefunction. The spatial VB configurations are defined in terms of the active orbitals only, and may be specified using one or more CON cards (note that the RESTRICT and SELECT keywords are not used in CASVB):

CON, $n_1,n_2,n_3,n_4,\ldots$;

The configurations can be specified by occupation numbers, as in section 13.4.3, so that $n_i$ is the occupation of the $i$th valence bond orbital. Alternatively a list of $Nact$ orbital numbers (in any order) may be provided - the program determines which definition applies. The two cards CON,1,0,1,2; and CON,1,3,4,4; are thus equivalent.

If no configurations are specified the single covalent configuration $\phi_1\phi_2\cdots\phi_{Nact}$ is assumed.