Vibronic model for mixed valence compounds and spin crossover systems

Abstract

The vibronic coupling model for mixed valence systems recently proposed by Piepho, Krausz and Schatz [1] is described. Using the model, it is a simple process to obtain the vibronic energy levels and eigenfunctions relevant to an intervalence band. Calculations are essentially exact within the context of the model, and are not limited to the cases of very strong or very weak interactions. The eigenvalues and eigenvectors obtained may be used to determine properties associated with the mixed valence band. These include, for example, the absorption profile of the band, the degrees of delocalization and valence-trapping, and the electron transfer kinetics for the system. Very similar formalism applies to both mixed valence and spin crossover systems. Thus the applicability of the model to single-center systems with two different spin states with intersecting potential surfaces is discussed. Finally, the limitations of the mixed valence model are discussed, and methods of improving the model by more explicit consideration of the nature of the interacting centers are considered.