K. B.  Sophy, Calaminici, P., and Pal, S., ?Density functional static dipole polarizability and first-hyperpolarizability calculations of Na-n (n=2, 4, 6, 8) clusters using an approximate CPKS method and its comparison with MP2 calculations?, Journal of Chemical Theory and Computation, vol. 3, no. 3, pp. 716-727, 2007.