ABINITIO SCF AND CEPA INVESTIGATIONS OF STABLE LITHIUM CLUSTERS

Various approaches of two Li2 molecules are investigated in a search for stable Li4 cluster configurations and favourable pathways forming them. The lowest energy minimum is found for a singlet state in a rhombic structure with its short diagonal close to the equilibrium internuclear distance of free Li2. The stability of this arrangement is traced to the binding potential of the p-π functions of its central Li2 substructure. This suggests a flat square bipyramidal configuration for Li6 which is indeed found to represent a local minimum. Binding energies for 2Li2 → Li4 and Li2 + Li4 → Li6 are calculated as 15 kcal/mole and 24 kcal/mole, respectively. Formation of both clusters is possible without surpassing energy barriers. Harmonic vibrational frequencies are given for Li4 and ionization potentials are calculated for Li4 and Li6. © 1979.