Calculation of phonon spectrum and elastic constants of FePd intermetallics: Performance of LDA and GGA

The phonon spectrum and elastic constants of L10 ordered FePd intermetallics have been calculated by first-principles density-functional perturbation theory using LDA and GGA approximations for the exchange-correlation part of the potential. The performances of the two functionals are compared by computing lattice dynamics at different volumes. The results are analyzed using relevant force constants. We find that the GGA at the experimental structure produces best agreement with the available neutron scattering results. This investigation provides a systematic understanding of the connections between the phonon spectrum and the inter-atomic interactions as well as of the ability of the different exchange-correlation functionals used in ab initio calculations in addressing them for FePd intermetallics. A strategy for modeling the inter-atomic interactions in FePd disordered alloys is also discussed based upon these results.