Lattice dynamics and Debye-Waller factors of some compounds with the sodium chloride structure

The lattice dynamics of 19 compounds with the sodium chloride structure hav e been investigated using shell models. The models are compared with: exist ing experimentally measured phonon-dispersion curves and refined using a mu ltidimensional downhill simplex method. Debye-Waller factors for these comp ounds are calculated over the temperature range from 1 to 1000 K where appr opriate and the results are fitted analytically using polynomial regression . The results are compared with experimentally measured room-temperature De bye-Waller factors and for most of the compounds the agreement is found to be better than 10%. At lower temperatures, it is expected that these result s would be more accurate, since the harmonic approximation, which is crucia l to the calculation of the Debye-Waller factors, works better. In choosing the models for particular applications, it is recommended that the model w ith the smallest standard error sigma is used for fitting the experimentall y measured phonon-dispersion curves, or the model that shows best agreement with reliable experimental measurements of more relevant physical quantiti es, such as Debye-Waller factors in crystallography.