LATTICE-DYNAMICS OF ALKALI-METALS IN REAL-SPACE

The two-body interaction is obtained in second-order perturbation theory following the procedure of Hafner and Heine. The interaction is then used to calculate the phonon spectrum, binding energy and elastic constants of alkali metals. The calculated values of phonon frequencies and elastic constants are found to be in reasonably good agreement with experimental results. The calculations are repeated using Pettifor and Ward ion-ion interaction and compared. The two pair potentials yield almost the same values of elastic constants. The results of phonon frequencies obtained using the two interactions are found to agree within 5% for all the metals except a few points near the Brillouin zone boundary. The pair potential due to Pettifor and Ward is found convenient for studying the dynamical and mechanical properties of the solids.