Analysis of the bonding and reactivity of H and the Al13 cluster using density functional concepts

The bonding of hydrogen in the Al13H aggregate is analyzed in the framework of density functional theory using the local density approximation. The interaction between the H-1s orbital and only certain molecular orbitals of Al-13 is responsible for the binding. Different measures of the charge transfer give consistent results and predict the stabilization of a sizable amount of electronic charge, about two electrons, around the proton site. The state of the H atom can be described as a negatively charged impurity screened by the surrounding electron gas, similarly to a H impurity embedded in a vacancy in metallic aluminum. Friedel-type oscillations can be appreciated in the screening charge. Local Fukui functions and condensed Fukui indexes associated to the ground state of the cluster Al-13 are used as indicators of molecular reactivity. Those indices allow to predict and understand the equilibrium location of H found in the total energy calculations for Al13H. (C) 2003 American Institute of Physics.