Vibronic coupling

The interaction between electronic states and states is called vibronic coupling (in discrete molecules) or electron-phonon coupling (in crystal systems or two- or three-dimensional systems). vibrational (or phonons). It has also been called the pseudo-Jahn-Teller effect, due to its conceptual relationship with the well-known Jahn-Teller effect.

This coupling has discernible consequences on the optical, magnetic, and electronic localization-delocalization properties in the molecule. Optically, the intervalnce band presented by mixed valence compounds becomes more complex and acquires a structure by vibronic coupling. Also the magnetic coupling is affected, if there are unpaired electrons in the system. Depending on the type of vibronic coupling that predominates, electronic delocalization can be enhanced or diminished.

Vibronic coupling models

Several models have been developed for the description of vibronic coupling, including:

• Hush model: Relatively simple, describes the optical consequences of the vibronic coupling, and relates the position and intensity of the interval band to microscopic parameters.
• Piepho-Krausz-Schatz (PKS): It is based on local vibrations, around the electroactive center. It is a quantum treatment, so it generates explicit wave functions.
• Piepho model: It is based on vibrations that modify the distances between electroactive centers. It is a quantum treatment, so it generates explicit wave functions.