where nelec is the total number of electrons, irrep is the number of the irreducible representation, and spin equals , where is the total spin quantum number. Instead of nelec also charge can be given, which specifies the total charge of the molecule. For instance, for a calculation in symmetry with 10 electrons, WF,10,3,0 denotes a state, and WF,10,1,2 a state. The charge can also be defined by setting the variable CHARGE:
This charge will be used in all energy calculations following this input. Note that SET is required, since CHARGE is a system variable (cf. section 8.4).
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.
If the WF directive is given outside an command input block, it is treated as global, i.e., the given values are used for all subsequent calculations. Setting the variables NELEC, SPIN, or SYMMETRY, has the same effect giving these on a global WF directive. If the global WF directive is given after the variable definition, the values of the variables are replaced by the values given on the WF directive. Vice versa, if a variable definition follows a global WF directive, the new value of the variable is used in the following. Note that WF input cards in command blocks have preference over global WF directives or input variables.