Ab initiostudy of low-energy collective electronic excitations in bulk Pb

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 electronic band structure calculated by means of a first-principles pseudopotential approach. The effect of inclusion of the spin-orbit interaction in the band structure on the excitation spectra in Pb is analyzed, together with dynamical exchange-correlation and local-field effects. In general, results show significant anisotropy effects on the dielectric response of bulk Pb. At small momentum transfers along three different high-symmetry directions, the calculated excitation spectra present several peaks with strong acousticlike dispersion in the energy range below 2 eV. The analysis shows that only one of such modes existing at momentum transfers along the $\ensuremath{\Gamma}$--$K$ direction can be interpreted as a true acousticlike plasmon, whereas all other modes are originated from the enhanced number of intraband electron-hole excitations at corresponding energies. Comparison with available optical experimental data shows good agreement.