Singlet excitations and dipole polarizabilities of Li2, Li4 and Li8 clusters

The ground state structure, singlet excitation energies, transition moments and static dipole polarizabilities together with the Cauchy coefficients are calculated for Li2, Li4 and Li8 using the coupled cluster response methods. Basis set and correlation effects are investigated for these properties. For the dipole polarizabilities the geometry effects are found to be particularly significant. The computed isotropic static dipole polarizabilities, approximately 209au for Li2, 333au for Li4 and 541au for Li8, and the calculated optical properties are generally in good agreement with experiment. For Li8, the results are obtained for the capped centred trigonal prism structure and for the tetrahedral structure. The first of these structures gives a more consistent description of the ground state properties of the cluster.