Phonons in solid argon

The phonon energies and the dynamic form factor, $S(\overrightarrow{\mathrm{Q}}, \omega )$, in solid ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$ at temperatures from 10 K to the melting point are calculated using the self-consistent-phonon (SCP) theory with the pair interaction represented by the recent realistic potential developed by Aziz and Chen. The temperature dependence of the phonon energies agree well with the observed values of Fujii et al. This is a substantial improvement over the previously available calculations obtained using anharmonic perturbation theory. The temperature broadening of $S(\overrightarrow{\mathrm{Q}}, \omega )$ also agrees well with the observed phonon groups for low-energy phonons where data are available and with the molecular dynamics (MD) calculations of Hansen and Klein. The $S(\overrightarrow{\mathrm{Q}}, \omega )$ for high-energy phonons near melting are found to be extremely broad, broader than in solid helium, and $S(\overrightarrow{\mathrm{Q}}, \omega )$ becomes very sensitive to intermediate phonon energies used in its calculation, making the present SCP group shapes not reliable for high-energy phonons near melting. Further experimental data or MD simulation of $S(\overrightarrow{\mathrm{Q}}, \omega )$ near melting for high-energy phonons would be most useful as a test of anharmonic theory, for example, of whether an explicit description of short-range correlations in the atomic motion is important.