MICROS — Generates only microstates with spin = n.




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 MICROS=1 specified, all of the spin adapted microstates used will have Sz = 1, i.e. two more alpha SOs occupied than beta SOs. For odd-electron systems with MICROS=1 specified, the spin adapted microstates used will have Sz = 3/2, i.e., three more alpha SOs 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 MICROS=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 MICROS=1 and CISTATE=n with n > 1, no doublet states will be generated.

See Chapter 11, Configuration Interaction for a more complete discussion of Ampac’s CI capability.





Default value:


See also:

C.I., SZ.