Singlet excitations and dipole polarizabilities of Li-2, Li-4 and Li-8 clusters

The ground state structure, singlet excitation energies, transition moments and static dipole polarizabilities together with the Cauchy coefficients a re calculated for Li-2, Li-4 and Li-8 using the coupled cluster response me thods. Basis set and correlation effects are investigated for these propert ies. For the dipole polarizabilities the geometry effects are found to be p articularly significant. The computed isotropic static dipole polarizabilit ies, approximately 209 au for Li-2, 333 au for Li-4 and 541 au f or Li-8, a nd the calculated optical properties are generally in good agreement with e xperiment. For Li-8, the results are obtained f or the capped centred trigo nal prism structure and for the tetrahedral structure. The first of these s tructures gives a more consistent description of the ground state propertie s of the cluster.