A Quantum Mechanical Study of Francium and Radium Clusters*

This report presents our research on the small atomic clusters of francium (Fr_n), and radium Ra_n (n = 1-9), and their hybrids Fr_nRa_n clusters. Francium is a heavy, unstable, radioactive metal with a maximum half-life of only 22 minutes. Radium is the heaviest and most reactive element of the alkaline earth metals family. Hybrid ab initio methods of quantum chemistry (particularly the DFT-B3LYP model) were used to derive optimal geometries for the clusters of interest. We compare calculated binding energies, bond-lengths, ionization potentials, electron affinities and HOMO-LUMO gaps for these clusters.The theoretical study of Fr_n clusters, such as ours, is particularly important because very little experimental data is available on its physical properties. It is interesting to check the stability of francium in cluster form. The interactions of Fr_n clusters with O atoms, O₂ molecules, H₂O molecules, and with some C_n clusters will be compared to similar interactions for Ra_n clusters. The possible implications of our computational results for the roles of Radium and Francium as cancer-causing materials will be examined.