Dynamical dipole and quadrupole response properties of small metallic particles: Random phase approximation and the modified spherical infinite barrier model

The self-consistent electrostatic response of small metallic spherical particles is studied in the random phase approximation and using the electronic wave functions in the infinite barrier model, with the size of the effective positive background adjusted to minimize the electrostatic energy of the system. The multipole susceptibilities and the numerical results are presented for the dipole (L = 1) and quadrupole (L = 2) cases. The spectra, showing both surface and several bulk plasmon peaks and the electron-hole excitations are discussed and analyzed in terms of their associated density fluctuations. The results are compared with the recent calculation of the same physical properties, based on the self-consistent field Kohn-Sham method.