Cold fusion: How close can deuterium atoms come inside palladium?

We use ab initio density functional calculations to determine the structural and electronic properties of deuterium in bulk palladium. The focus of our study is the binding and the nearest-neighbor distance between D atoms in the very concentrated limit of a hypothetical ${\mathrm{PdD}}_2$ crystal. These results are compared to analogous calculations for bulk PdD and Pd. We find that even at very high D concentrations in the bulk, the equilibrium distance between two D atoms is increased by ≊0.2 Å from the gas value of 0.74 Å. This large internuclear distance makes a cold-fusion reaction of deuterium very improbable.