Data Analysis and DOS Example Hexacyanoferrate

Using normalization properties of the polarization vectors one obtains [83, 89]  

The composition factor for the acoustic branch of the NIS spectrum is derived from (9.10) by assuming (in the approximation of total decoupling of inter- and intramolecular vibrations) that the msd in acoustic modes are identical for all the atoms in the molecular crystal  

The highest possible composition factor Cmax for a given molecule is 

Assuming that the resonant atom belongs to a rigid molecular fragment with mass Ml, which exhibits stretching against the rest of the molecule, the composition factor for this stretching mode is 

If a vibrational mode is not a pure stretching mode but contains bending contributions, the composition factor may deviate from in both directions. 

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