BARRIER FOR THE REACTION X(20-]X(40)2+ IN ALKALI-METAL CLUSTERS RELATED TO ELECTRON-DENSITY AT THE BOND MIDPOINT OF THE SUPERMOLECULE (X(20+))2()+X(20+))

Using the extended Thomas-Fermi version of density-functional theory ( DFT), calculations are presented for the barrier for the reaction Na20 ++Na20+-->Na-40(2+). The deviation from the simple Coulomb barrier is shown to be proportional to the electron density at the bond midpoint of the supermolecule (Na20+)2. An extension of conventional quantum-ch emical studies of homonuclear diatomic molecular ions is then effected to apply to the supermolecular ions of the alkali metals. This then a llows the Na results to be utilized to make semiquantitative predictio ns of position and height of the maximum of the fusion barrier for oth er alkali clusters. These predictions are confirmed by means of simila r DFT calculations for the K clusters.