On third-order elastic constants for ductile rare-earth intermetallic compounds: A first-principles study

We present the unknown third-order constants of ductile rare-earth intermetallic compounds YAg and YCu with CsCl-type B2 structure. Density functional theory (DFT) within generalized-gradient-approximation (GGA) combining with the method of homogeneous deformation is employed. The predictions for the elastic constants are obtained from a polynomial fit to the calculated strain–energy relation from first-principles total-energy calculations. Calculated second-order elastic constants are consistent with the previous calculations and the experiments. The third-order effects really matter when the finite strains are larger than approximately 3.0%. The relation between the third-order elastic constants and pressure derivatives of the second-order elastic constants has also been discussed.