Theoretical Expression, C sub 44 = 1/3(2C sub 11 --C sub 12 ), in Better Agreement With Experiment Than the Cauchy Relation C sub 44 = C sub 12 for F.C.C. Crystals

The formalism developed by Milstein and Hill to compute the elastic properties of cubic crystals under pressure is used to show that C sub 44 = 1/3(2C sub 11 --C sub 12 ) for models of f.c.c. crystals which allow for complications of atomic binding, but in which nearest neighbor interactions determine the values of the elastic moduli. This relation is in better agreement with experimental data for metals and inert gas solids than the Cauchy relation C sub 44 = C sub 12 . Also, pseudopotential computations of the elastic moduli of Cu and Ag provide theoretical support for the efficacy of the model under high (as well as atmospheric) pressure. 31 ref.--AA