Dynamic polarizability of small simple metal clusters in dielectric media.

Abstract

The dipole dynamic polarizability of small sodium and aluminum jelliumlike clusters embedded in different dielectric media has been calculated using the time-dependent density-functional method with the frequency-dependent local exchange-correlation potential. The matrix has been taken into account through a static dielectric constant \ensuremath{\varepsilon}. Photoabsorption resonances obtained within the density-functional theory are redshifted with respect to the position of the classical surface plasmon for a metal sphere of the same size within the same matrix. As \ensuremath{\varepsilon} increases, photoabsorption resonances shift to lower energies. We have discovered that the peaks caused by one-electron transitions and by collective excitations move to lower energies at different rates. For sodium clusters, the surface plasmon shifts more slowly than one-electron resonances; for aluminumlike clusters, the reverse is observed. In the case of sodium, this leads to the displacement of the surface plasmon from the region below the continuum threshold (when the cluster is in vacuum) to the continuum of states (for the cluster embedded in a dielectric). \textcopyright{} 1996 The American Physical Society.