Noncentral force model for h.c.p. metals

The elements of the dynamical matrix are separated into two parts : (i) a short-range closed-shell part and (ii) an ionic part. The effect of the former is calculated using noncentral forces involving central as well as angular forces whereas the latter part is evaluated on the lines of Krebs using a screened Coulomb potential. The calculated phonon frequencies along symmetry directions and θ–T curves for Mg, Be, and Tl have been plotted and compared with the experimental results.