##

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 2020-02-28