Linear potential and phonons in alkali-metals

Phonon dispersion, binding energy, compressibility and elastic constants of alkali-metals have been studied using a modified form of the Ashcroft potential and self-consistent form of electron screening due to Singwi et al. The proposed potential successfully reproduces the phonon spectra and other properties of all the five metals except for the crossover between Δ1 and Δ5 branches for lithium —which may be attributed to the very small amplitude of the form factors atq=2kF. An improvement corresponding to this effect could reproduce Kohnanomaly and the crossover simultaneously.