The energy of interstitial hydrogen in α-zirconium

Neutron diffraction experiments indicate that hydrogen enters α-zirconium interstitially. The relative energies of hydrogen in tetrahedral and octahedral interstitial sites of the h. c. p. lattice are calculated assuming that the energy terms most strongly dependent on the site symmetry are the electronic and protonic electrostatic contributions. The calculations show that the tetrahedral site is preferrred, in agreement with experiment. The effects of lattice distortions near a proton are shown to be unimportant in determining the site preference.