Valence-Rydberg mixing

The extensive calculations of Serrano-Andres et al [31] have shown a spurious valence-Rydberg mixing in the CASSCF wave functions when valence (7t,7r )and Rydberg orbitals are optimized all together in a state average calculation it was shown that these orbitals loose their diffuse character and instead tend to provide an extra correlation to valence orbitals. To avoid such interaction, the orbitals used for the Cl treatment of the electronic spectrum were obtained by a two step procedure ... 

Most frequently interactions between states of the same electronic symmetry are between a Rydberg state and a valence state and are often referred to in the literature as valence Rydberg mixing. In the following, a distinction is drawn between these two classes of electronic states. 

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