The E2g phonon and the elastic constant C44 in hexagonal van der Waals bonded solids

A simple relation between the frequency of E-2g phonon modes and the elastic constant C-44, derived previously for hexagonal-close-packed metals, is found to be reasonably valid for crystals of solid He, H-2, D-2 and N-2 at or near normal pressure. Good agreement at high pressure for n-H-2 suggests that the connection between C-44 and the phonon frequency also holds over a wide compressional range.