Made-to-measure potential functions in lattice dynamics—solid Cl2

A simple method is outlined for identifying potential functions designed to reproduce given normal mode frequencies, equilibrium conditions and other constraints. It is applied to a model of solid Cl2 and a family of potentials found which satisfy a large number (14) of constraints but which have other, implausible features. The application is presented as a cautionary illustration of Szigeti's theorem [2]. A more useful area of application is seen to be in refining potentials whose principal features are already known.