##

4.9 Defining the wavefunction

In all program modules where such information is required, the total symmetry of the
-electron wavefunction is defined on `WF` (wavefunction) cards in the following
way:
`WF`,*nelec,irrep,spin*

or, alternatively

`WF`,[`NELEC=`*nelec*],[`SYM[METRY]=`*irrep*],[`spin=`*spin*],[`CHARGE=`*charge*]

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`:

`SET,CHARGE`=*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.

molpro@molpro.net 2019-05-25