Comments on the elastic properties in solid solutions of silver halides

Recently first principles microscopic calculations, using the generalized gradient approximation, appeared for the solid mixed system $AgCl{_x}Br_{1-x}$ at various compositions. Here, we suggest a model that can estimate the compressibility of the mixed crystals in terms of the compressibilities of the end members alone. This model makes use of a single parameter, i.e., the compressibility of a defect volume, when considering the volume variation produced by the addition of a "foreign molecule" to a host crystal as a defect volume.