6.14 Defining the wavefunction

In all program modules where such information is required, the total symmetry of the $N$-electron wavefunction is defined on WF (wavefunction) cards in the following way:

WF,nelec,irrep,spin

where nelec is the total number of electrons, irrep is the number of the irreducible representation, and spin equals $2 \times S$, where $S$ is the total spin quantum number. For instance, for a calculation in $C_{2v}$ symmetry with 10 electrons, WF,10,3,0 denotes a $^1B_2$ state, and WF,10,1,2 a $^3A_1$ state.

Although in principle each program unit requires a WF command, in practice it is seldom necessary to give it. The program remembers the information on the WF card, and so one might typically specify the information in an SCF calculation, but then not in subsequent MCSCF or CI calculations; this also applies across restarts. Furthermore, nelec defaults to the sum of the nuclear charges, irrep to 1 and spin to 0 or 1; thus in many cases, it is not necessary to specify a WF card at all.