PHONON FREQUENCIES OF ALKALI METALS

Phonon frequencies of alkali metals are calculated using the single orthogonalized-plane-wave electron-ion matrix element and the dielectric functions due to Singwi et al. and to Geldart and Vosko. We have calculated the bare-ion potential by the Hartree-Fock-Slater method, where the Slater exchange potential is replaced by a modified Kohn-Sham exchange potential which approximates correlation effects according to the simple prescription of Robinson et al. The calculated phonon frequencies of Li, Na, K, and Rb are in good agreement with the neutron spectroscopy measurements. © 1969 The American Physical Society.