Name
SZ — Specify value of Sz.
Description
For a set of spin adapted microstates which is degenerate in both spin multiplicity and
energy, only a single member of the set is included in the expansion of the CI eigenstates. By
default, the spin adapted microstate with the smallest non-negative Sz
eigenvalue is chosen, i.e., Sz = 0 for systems with an even number of
electrons and Sz = 1/2 for systems with an odd number of electrons.
This behavior can be overridden using this keyword, where the value of
Sz used will be shifted by n from the default value. For example, for
even-electron systems with SZ=1 specified, all of the spin adapted microstates used will have
Sz = 1, i.e. two more alpha spin orbitals occupied than beta spin
orbitals. For odd-electron systems with SZ=1 specified, the spin adapted microstates used will
have Sz = 3/2, i.e., three more alpha spin orbitals occupied than beta
SOs. Of course, the value of Sz desired should not exceed the total
spin corresponding to the specified spin multiplicity keyword. For example, specifying
DOUBLET together with SZ=1 will not work
because a doublet eigenstate cannot be expanded in terms of quartet microstates. For the same
reason, if QUARTET is specified along
with SZ=1 and CISTATE=n with
n > 1, no doublet states will be generated.
Default value:
0 with even number of electrons; ½ with even number of electrons
