A New Analysis of Slater's Compressibility Data

Abstract

The variation of interatomic forces with interatomic distances in crystals may be determined empirically from compressibility data. The experimentally possible range of variation in interatomic distance is, however, so small that the form of the force function valid for extrapolation to much greater distances cannot be adequately determined. From an analysis of Slater's compressibility data for the alkali halides it appears that for them the interionic forces of repulsion may be derived from a common force function. Because of the relatively large variation of lattice constant between the different alkali halides it is possible to determine a form for this common force function which is valid for relatively large variations in interatomic separation. The force function so found differs but little from the inverse power or from the exponential forms for small displacements from the equilibrium position. It drops off more rapidly, however, for increasing distances and increases more rapidly for decreasing distances. The solution given has the interesting property that of all possible force functions compatible with Slater's compressibility data it is the least favorable for the formation of a secondary structure.