Theory of hydrogen pairing in metals

Abstract

The nature of hydrogen-hydrogen interaction in simple lithium, aluminum and transition (yttrium, palladium) metals has been studied by calculating, self-consistently, the energetics and electronic structure of hydrogen pairs as a function of their interatomic separation. While the formation of molecular bonds between hydrogen atoms in metals is possible, it is shown that hydrogen prefers to optimize its bonds with metal atoms, and in some cases, such as rare earth metals, hydrogen pairing mediated by the metal atom may be energetically preferable. The metal-hydrogen bond is characterized by charge transfer from metal atoms to hydrogen while the hydrogen atoms involved in the molecular bond in the metal are neutral. The energy barrier between the two kinds of bonding minima is found to be dependent on the number of metal atoms in the embedding medium. The consequences of this observation in explaining the temperature dependence of proton spin-lattice relaxation time in metals vs . organometallic complexes are discussed.