Theory of Fe, Co, Ni, Cu, and their complexes with hydrogen in ZnO

The properties of a range of $3d$ transition metals and their complexes with hydrogen are studied using local-density-functional methods. The location of the impurity-related $3d$ bands strongly affects the electronic and magnetic properties of both substitutional and interstitial impurities, with high spins being preferred in line with Hund's rule. The relative formation energies of the defects are considered and the favorable defect for various growth conditions under equilibrium discerned, indicating strongly bound impurity pairs and impurity-hydrogen complexes. H-related local vibrational modes are compared with experimental observations, and in particular models proposed in the literature for CuH complexes have been examined.