Lattice Dynamics of fcc Argon with Three-Body Forces

Phonon spectra are calculated for fcc ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ at 4, 40, and 77 °K using the pair potential for argon atoms derived by Bobetic and Barker. The calculation employs a quasiharmonic basis with three-body forces and a perturbation-theory treatment of the anharmonicity. Poor agreement is obtained with the experimental temperature shifts of transverse phonons propagating along the $\left[\xi 00\right]$ direction. Self-consistent phonons are also calculated at 0 °K for both the Bobetic-Barker and Dymond-Alder potentials. On the basis of existing phonon data, the latter appears to be ruled out as a realistic pair potential.