Interaction of hydrogen atoms with small magnesium clusters doped with aluminum and 3d transition metals

Abstract

Model calculations based on extended Huckel molecular orbital theory are presented for the approach of hydrogen atoms to Mg 3-M-Mg 3 clusters, where M ≡ Mg, Al, Ti, V, Cr and Mn. The resulting double-welled potential curves serve as a basis for qualitative speculation on the rates of hydriding and dehydriding and the thermal properties of doped magnesium metal hydrides. The stabilities of isolated Mg 3-M-Mg 3 metal clusters, with magnesium atoms fixed at distances characteristic of the magnesium metal lattice, are examined for M ≡ Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. Clusters for which M ≡ Mg, Ti, V, Cr, Mn and Fe are found to be stable with respect to the isolated atoms, while clusters for which M ≡ Co, Ni and Cu are unstable in this particular geometry. The presence of the doping atom in all cases decreases the work function of the magnesium cluster (as estimated by Koopmans' theorem). In contrast, the presence of hydrogen in most cases increases the work function of the metal cluster.