Lattice Dynamics of NaF

The results of an extended calculation of the normal modes of the NaF lattice are presented. Three models have been considered: a "rigid-ion" (RI) model, a "deformation-dipole" model with central F^--F^- short-range interactions (DDNNN), and a "deformation-dipole" model including both central F^--F^- interactions and a noncentral component in the first-neighbor, short-range interactions [DDNNN(NC)]. For each of these models we have derived frequency spectra for both 300 and 0^∘{}K input parameters, the associated dispersion curves for symmetry directions, Debye characteristic temperatures ΘD, moment functions ωD(n), and the Na⁺ and F^- Debye-Waller parameters B₁ and B₂ and their ratio B₁B₂. Of the three models, the two DD variations give good agreement with the observed dispersion curves, the DDNNN models being slightly better and giving somewhat closer agreement with the observed B values.