The H-H interaction potential in ${\mathrm{Pd}}_{\mathit{x}}$${\mathrm{H}}_2$ (x=2,4) clusters is investigated by means of ab initio Hartree-Fock techniques. Both linear arrangements and spatial configurations, in which the H-H bond is taken perpendicular to the line, or plane, of the Pd atoms, are considered. The Pd-Pd distances are kept fixed while the H-H potential-energy curves are calculated. Only the linear geometry allows a reduction of the H-H distance with respect to the gas phase. Fusion rates are calculated for the latter geometry. Our results show that, even for the unrealistic situation in which the two H atoms are in between two Pd atoms at the shortest distance found in the metal (5.2 a.u.), the fusion rate (${10}^{\mathrm{-}56}$) is far below the values inferred by some authors from experimental data.

• Received 5 March 1990

DOI:https://doi.org/10.1103/PhysRevB.42.4996