Static electric dipole polarizabilities of alkali clusters

We have measured the static dipole polarizability of lithium and sodium clusters (n = 1 - 22). Values measured for sodium are in agreement with previous experiments. While the polarizability per atom for sodium clusters decreases slowly as a function of the cluster size, a sharp decrease between sizes 1 and 4 is observed for lithium clusters. Experimental values are compared to Density Functional Theory (DFT/PWS1) calculations. The size evolutions for sodium and lithium cluster polarizabilities are well reproduced by our calculations. The sharp decrease observed for small lithium clusters is discussed in terms of electronic density.