Theory of the NiH₂ complex in Si and the CuH₂ complex in GaAs

Spin-polarised local density functional cluster calculations are carried out on substitutional Ni in Si and Cu in GaAs along with TM-H₂ complexes. The Jahn-Teller distortion for Ni in Si leads to a slight displacement along ⟨100⟩ in agreement with EPR experiments. Several models of NiH₂ are investigated and it is shown that one, with H located at anti-bonding sites to two of the Si neighbours of Ni, has the lowest energy and possesses H related local vibrational modes close to those reported for Pt-H₂. A similar structure is found for CuH₂ in GaAs. The electronic properties of the complexes are described in terms of the vacancy model of TM impurities.