Lattice Dynamics of Diamond

The first two authors have measured the dispersion curves for phonons whose wave vector lies along the symmetry lines $\Sigma$ and $Z$ in the Brillouin zone. The measurements were made by the method of inelastic neutron scattering. With the aid of these new results the latter two authors have determined the shell-model parameter $\delta$ which could not be determined from the previously measured dispersion curves along the lines $\Delta$ and $\Lambda$. A figure is given which summarizes all the measured dispersion curves of diamond and gives the most recently calculated shell-model fit to the data. Because of the large size of this parameter $\delta$, it was necessary to recompute some of the thermodynamic and optical properties of diamond previously reported by the last two authors elsewhere. Thermodynamic quantities such as the Debye temperature were very little affected, but some of the critical-point frequencies used in the analysis of the two-phonon infrared absorption spectrum had to be altered. A corrected table of critical points is given.