Stable (Na19)2as a giant alkali-metal–atom dimer

We report that a dimer of clusters, (${\mathrm{Na}}_{19}$ ${)}_2$, is energetically stable and explains the abundance of ${\mathrm{Na}}_{38}$ in sodium-cluster mass spectra. A fusion process of two ${\mathrm{Na}}_{19}$ clusters has been studied on the basis of the jellium-sphere-background model by the local-spin-density-functional method. Calculated binding energies show that the force between two clusters is attractive and that the complete fusion is preceded by the formation of a stable (${\mathrm{Na}}_{19}$ ${)}_2$, whose electronic structure is analogous to an alkali-metal–atom dimer, supporting the concept of ‘‘clusters of giant atoms’’ for sodium clusters.