The relative stabilities of H at (or near to) the tetrahedral interstitial and bond-centered sites, as well as those of H dimers in the molecular and bond-centered anti-bonding configurations, were calculated at the  ab initio  level in molecular clusters in crystalline C, in -phase Sn and in the semiconductors. The trends showed that the lowest-energy configurations changed in going down the periodic table. The relative stability of the possible equilibrium sites affected which charge states of H were likely to appear in a given host: This, in turn, affected the diffusion properties of H and its interaction with dopants and other defect centers. The trends in the equilibrium geometries and relative stabilities showed that Si was a special case, among group-IV hosts, in which both isolated interstitials and both dimer states were close to each other in energy. The properties of 2 charge states in molecular H in Si were examined in order to determine the key features of their electron paramagnetic resonance spectra.

S.K.Estreicher, M.A.Roberson, D.M.Maric: Physical Review B, 1994, 50[23], 17018-27