H 2 Dissociation in Nickel. A Cluster Model

A cluster formed by 38 Ni atoms and two H atoms is studied by a semiempirical Hartree‐Fock (HF) self‐consistent‐field (SCF) variant based on the INDO (intermediate neglect of differential overlap) approximation. The energy of the system is analyzed as a function of the spatial localization of the two H atoms. The energy minimum in the considered part of the singlet‐type potential surface corresponds to a spatial arrangement where the H atoms occupy nearest‐neighbor octahedral sites in the f.c.c. Ni‐lattice ( d (HH) = 0.249 nm). This configuration is ≈ 1 eV below another local minimum which is associated to a “H 2 ” molecule ( d (HH) = 0.085 nm) in the host system. The H atoms in the Ni‐lattice can be characterized as overscreened protons.