Nearest-neighbor interaction model excitation

The next natural step is the discussion of Fermi resonance effects in molecular crystals. Let molecules having Fermi resonance between intramolecular vibrations form a molecular crystal due to weak (van der Waals) forces. Then the individual molecular vibrational excitations discussed above become coupled to each other and form collective Fermi resonance bands. We shall consider here a simple two-layer ID model with intermolecular interaction only between nearest neighbors (see Fig. 9.6). 

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