The Deformable Shell Model Calculation of Infrared Absorption Frequencies of Ionic Crystals

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Abstract
The deformable shell model which includes many‐body effects and accounts for the breakdown of Cauchy relation is extended to the case of the CsCl structure. The TO mode frequencies for q = 0 are calculated for eight ionic crystals of both NaCl and CsCl structures. For comparison, the shell model values are also calculated. The results are compared with the infrared absorption frequencies. It is found that the deformable shell model gives better agreement than the shell model. The result is particularly striking for crystals showing a large Cauchy relation breakdown.