Mixed-valence Piepho-Krausz-Schatz model

Piepho-Krausz-Schatz Model and Robin and Day Classification of Mixed-Valence Compounds... 

Ln = A general abbreviation for lanthanide elements PKS model = The model developed by Piepho, Krausz, and Schatz for treating the electronic structure of mixed valence compounds. 

Following the work of Robin and Day, and Allen and Hush, the first rigorous solution to the vibronic Schrddinger equation for a mixed valence system was formulated by Piepho, Krausz, and Schatz. This model, based on the valence bond approach, is known as the PKS model. It is a model that has been modified to include orbital vibronic constants. A frilly equivalent molecular orbital model developed by Piepho is easier to conceptualize, however. The Piepho model also was the first to take advantage of the concept of orbital vibronic constants developed by Bersuker for Jahn-Teller systems (Figure 4). The Jahn-Teller theory is the basis for the PKS model. 

This model was originally used along with the Day-Hush disproportionation model, mentioned in Section 10.7.2, and got its name from the pioneers S. Piepho, E. Krausz, and P. N. Schatz (PKS). The PKS model is a useful and consistent model for the treatment of spectra of mixed valence systans. The model includes the vibrational levels for MV-2 and MV-3 systems. It is assumed that the coupling is small so that the harmonic approximation can be used. 

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