Electron transfer optical bands of charge-ordered mixed valence compounds. Quasidynamical model

An approximate quasidynamical model is proposed to describe electron transfer bands of mixed-valence charge-ordered crystals. Within the scope of this model the adiabatic approximation is employed for order parameter calculation. The dynamical (quantum-mechanical) single-cluster problem is solved in the molecular field approach. The electron-transfer (intervalance) optical band shape is investigated in detail for different phase states of a mixed-valence crystal. Intervalence absorption band shape and position provide important data on key parameters of mixed-valence cystals, i.e. double exchange, vibronic and intercluster interaction parameters. Comparison of results obtained for the semiclassical and quasidynamical models is presented for different values of vibronic coupling, double exchange and intercluster interaction. The semiclassical approximation is shown to be not applicable for the description of some important spectral regions of intervalence bands.