Range of forces on host-metal atoms around interstitial hydrogen in Pd and Nb

Forces on the host-metal atoms surrounding a hydrogen atom at different interstitial positions in palladium and niobium are calculated from first principles in the local-density approximation with a mixed-basis pseudopotential supercell approach. For supercells ${\mathrm{Pd}}_{\mathit{n}}$H (n=1,4,8,16,32) previously reported results are reanalyzed and corrected based on a recently noticed simplification in the computational method. Results are presented for supercells ${\mathrm{Nb}}_{\mathit{n}}$H (n=1,2,4,8,16). In both elements the displacement forces decay dominantly within the range of one lattice constant. The elastic force-dipole tensors are determined from the first-principles forces. The results for octahedral occupation of H in Pd and tetrahedral occupation of H in Nb support the picture of static occupation of distinct interstitial sites.