Density functional calculations on hydrogen in palladium-silver alloys

Periodic bulk calculations based on density functional theory within the generalized gradient approximation (GGA) have been used to calculate properties of the palladium-silver metals and alloys Pd4-nAgn (n = 0-4) with and without absorbed hydrogen. For each of the metals and alloys, we have calculated the equilibrium lattice constant, the preferred hydrogen absorption site, the absorption energy as a function of hydrogen content (indicating the hydrogen solubility), and the equilibrium lattice constant of the resulting metal hydrides. Most of the results are qualitatively in good correspondence with experimental data, showing that periodic electronic structure calculations like this may be useful in understanding qualitative properties of disordered alloy-hydrogen systems, We are not able, however, to obtain satisfactory results for the cohesive energy and the absorption energy of hydrogen in pure silver. The former is a known failure of the GGA functional that we have used, while the latter could most probably be resolved by lattice relaxation. (C) 2002 Elsevier Science BY All rights reserved.