The cohesive energy density and the isothermal compressibility: Their relationships with the surface tension

Models for predicting the cohesive energy density (CeD), the isothermal compressibility (kT), the compressibility and surface tension product (kT.γ  ), the ratio of surface tension to cohesive energy density (γ/CeD)(γ/CeD) and the isothermal compressibility and cohesive energy density product (kT.CeD) are described. The temperature T at which the numerical constants are valid is the melting temperature. The studies are being restricted to alkali halides. The calculated (kT.γ) values (21.3–40.9 pm), pertained to the sizes of voids between the ions, are of a smaller range than in the earlier treatments and agree very well with the experimental published data (21.9–47.6 pm). The determined (γ/CeD)(γ/CeD) values (4.3–8.2 pm), attributed to the contraction of the internuclear distance of the top-layer atoms in the surface, are comparable with the experimental data (3.9–11 pm). It is found that the ratio of the internuclear distance at the surface to that of the bulk is 97–98%.