Ab initio study of low-energy electronic collective excitations in bulk Pb: anisotropy and acoustic modes

Abstract

A theoretical study of the dynamical dielectric response of bulk lead at low energies is presented. The calculations are performed with full inclusion of the electron band structure calculated by means of a first-principles pseudopotential approach. The effect of including the spin-orbit splittings in the band structure is analyzed, together with dynamical exchange-correlation and local-field effects. Excitations are studied in detail, showing the presence at small momenta of acoustic-like dispersing excitations. The character of these modes with sound-like dispersion depends on the direction of the momentum transfer q. In general results show strong anisotropy effects on the dielectric response of bulk Pb. Comparison with available optical experimental data shows good agreement.