Interstitial-electron model for the lattice dynamics inNi3Al

We extend and test the applicability of an interstitial-electron model to calculate the lattice dynamics in a close-packed alloy system. The key element in the model is the use of classical particles in tetrahedral interstices in the lattice to treat electronic degrees of freedom. The calculations involve only central-force pair potentials between particles representing the atoms and electrons. All pair interactions up to a nearest-neighbor metal-metal distance are included to fit the lattice dynamics of ${\mathrm{Ni}}_3$Al. The calculated phonon dispersions are in excellent agreement with experiment.