Multiple deuterium occupancy of vacancies in Pd and related metals

The binding energies of up to six deuterium atoms into monovacancies of Pd, Ni, Fe, Cu, Nb, and Mo have been calculated using the effective-medium theory. For all metals it is found that at least six D atoms can be accommodated in the vacancy. Of the systems studied the deuterium-deuterium interaction is found to be least repulsive for Pd. This multiple occupancy of the vacancy defect can have potentially significant implications for the recently proposed fusion of D atoms in Pd.