Optical response of bimetallic Li _x Na_8−x (0≦x≦8) and of doped Na₈Zn clusters

Abstract

Using the time dependent local density approximation we calculate the photoabsorption spectra of bimetallic Li _x Na_8−x (0≦x≦8) and of doped Na₈Zn clusters. Ground state cluster geometry and electronic structure are obtained by minimization of total energy from Kohn-Sham self-consistent calculations within the spherically averaged pseudopotential method. For Li _x Na_8−x clusters we obtain two nearly isomeric geometries. In both cases the corresponding photoabsorption spectra show a single collective excitation (surface plasmon) at increasing frequency as the number of lithium atoms increases. For a given number of lithium atoms, the plasmon frequency of the cluster in the ground state geometry is ~ 0.1 eV blueshifted with respect to that in the isomeric state. The equilibrium geometry of doped Na₈Zn cluster is formed by a nearly spherical shell of eight Na atoms enclosing the Zn impurity at the cluster center. The corresponding optical spectrum shows two peaks at higher frequencies than the surface plasmon of pure Na₈ cluster, in agreement with recent photodepletion spectroscopy experiments.