Configuration interaction excited states

One approach is to construct a more flexible description of electron motions in terms of a combination of Hartree-Fock descriptions for ground and excited states. Configuration interaction (Cl) and Moller-Plesset (MP) models are two of the most commonly used models of this type. The so-called second-order Moller-Plesset model (MP2) is the most practical and widely employed. It generally provides excellent descriptions of equilibrium geometries and conformations, as well as thermochemistry, including the thermochemistry of reactions where bonds are broken and formed. Discussion is provided in Section n. 

Eleven of these can house the 22 electrons of Ng in its ground state the rest can serve as virtual orbitals for excited states in rough calculations or to improve the ground-state wavefunction by mixing it with that of excited states [configuration interaction). In order to obtain more reliable wavefunctions for excited states the basis set must be expanded. 

So, one-electron transitions between Gouterman s two new HOMOs (now accidentally degenerate) and two LUMOs, generates four degenerate electronically excited states. Configuration interaction then mixes them to give a sum and a difference of intensities which were originally equal. 

Calculation of Electronic Excited States Configuration Interaction (Cl) Procedure. 69... 

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