OPTICAL-RESPONSE OF BIMETALLIC 0-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-8) AND OF DOPED NA8ZN CLUSTERS

Using the time dependent local density approximation we calculate the photoabsorption spectra of bimetallic LixNa8-x (O less-than-or-equal-t o x less-than-or-equal-to 8) and of doped Na8Zn clusters. Ground state cluster geometry and electronic structure are obtained by minimizatio n of total energy from Kohn-Sham self-consistent calculations within t he spherically averaged pseudopotential method. For LixNa8-x clusters we obtain two nearly isomeric geometries. In both cases the correspond ing photoabsorption spectra show a single collective excitation (surfa ce plasmon) at increasing frequency as the number of lithium atoms inc reases. For a given number of lithium atoms, the plasmon frequency of the cluster in the ground state geometry is approximately 0.1 eV blues hifted with respect to that in the isomeric state. The equilibrium geo metry of doped Na8Zn cluster is formed by a nearly spherical shell of eight Na atoms enclosing the Zn impurity at the cluster center. The co rresponding optical spectrum shows two peaks at higher frequencies tha n the surface plasmon of pure Na8 cluster, in agreement with recent ph otodepletion spectroscopy experiments.