NON-CENTRAL FORCE MODEL FOR THE LATTICE-DYNAMICS OF CUBIC METALS

A noncentral force model for the lattice dynamics of cubic metals is propounded by taking into account the volume forces (electron-ion interaction) and the angular forces of the type suggested by de Launay and Clark et al. in addition to the usual central forces. The electron-ion interaction is formulated through the Krebs theory. The secular equation contains five constants which are determined from the three elastic constants and two zone-boundary frequencies. The model is applied to calculate the phonon dispersion curves, frequency distribution functions, and heat capacities of alkali metals. The results show satisfactory agreement with the neutron scattering and calorimetric data. It is shown that the two angular forces are equivalent for calculating the lattice frequencies of body-centered-cubic metals. © 1979 The American Physical Society.