Pressure dependence of phonon dispersion curves in simple metals

The reliability of different forms for the bare electron-ion model pseudo-potential and for the dielectric screening function has been studied by calculating, at variable volume, phonon dispersion curves in the simple metals sodium, aluminium and lead. It is found that inclusion of exchange and correlation effects in the dielectric function is essential for agreement with experiment. Pressure derivatives of the elastic constants for these metals, as predicted from the Heine-Abarenkov potential, are reasonably accurate, while the pressure derivatives of the maximum phonon frequencies yield good qualitative agreement with the experimental pressure derivative of the superconducting transition temperature in aluminium.