Complex configuration interaction

Complex Configuration Interaction (CCI). A logical extension of the CSCF Idea Is complex Cl with a CSCF reference configuration. The trial function Is now... 

Configuration interaction, which is necessary in treatments of excited states and desirable in calculations of spin densities, is more complex with open-shell systems. This is because more types of configurations are formed by one-electron promotions. These configurations (Figure 5) are designated as A, B, Cq, C(3 G is the symbol for a ground state. Configurations C and Cp have the same orbital part but differ in the spin functions. 

The lowest excited states of paramagnetic metal complexes are described by configuration interactions of the porphyrin (7T,tt ) excited singlet and triplet states and the "porphyrin-to-metal" or metal-to-porphyrin charge-transfer excited states (35,36). Thus T (phosphorescence) emission of paramagnetic metal complexes decays... 

Overall, we seem to find reasons to be hopeful about the possibilities of the RQDO formalism for predicting spectral properties of complex atoms. Very recently, some lifetime calculations in Yb 11 have also been successfully performed [30]. These reasons rest on the correctness of the results so far obtained, as well as the low computational expense and avoidance of the frequent convergence problems that are common in configuration interaction approaches. 

The simplest and most widely-employed method is the so-called configuration interaction singles or CIS method. This involves singleelectron promotions only (from occupied molecular orbitals in the reference wavefunction to unoccupied molecular orbitals). Because there are relatively few of these, CIS is in fact practical for molecules of moderate complexity. As noted previously, single-electron promotions do not lead to improvement in either the ground-state wavefunction or energy over the corresponding Hartree-Fock... 

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