Anharmonic phonons in Cs

The dynamic form factor $S(\overrightarrow{\mathrm{Q}},\omega )$ and the phonon frequencies and lifetimes in Cs at $T=5,90\mathrm{}$, and 290 K are calculated. The anharmonic properties of Cs are apparently dominated by the cubic anharmonic term. Properties such as anharmonic interference in $S(\overrightarrow{\mathrm{Q}},\omega )$ which is proportional to the cubic term are found to be relatively large and should be readily observable at high temperature. The most interesting phonons are the longitudinal phonons along the [100] direction at high $Q$, which have the shortest lifetimes, and the $T_1$ phonons along [110] which are very sensitive to anharmonic contributions.