Many‐body effects on the third‐order elastic constants and pressure derivatives of the second‐order elastic constants of CsCl structure solids

Abstract

AbstractLundqvist's potential for ionic solids is used to derive expressions for the second‐order elastic (SOE) constants and the third‐order elastic (TOE) constants. It is observed that the Cauchy relations among these constants do not hold even at 0 K and the discrepancies in this relation are directly expressible as function of the many‐body term in the crystal potential. It is demonstrated that all parameters except one appearing in the expressions for the TOE constants and pressure derivatives of the SOE constants can be calculated from the values of the SOE constants, the equilibrium condition, and an approximate assumption concerning the overlap repulsion. Determining the remaining parameter (a2∂2ƒ/∂r2)0 from the expression of the pressure derivative of the bulk modulus all the six TOE constants and the remaining pressure derivatives of the SOE constants can be calculated. The values so obtained approach quite close to the measured values as against those of other theoretical workers in all the cases in which experimental results are available.