SZ — Specify value of Sz.




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

See also: