Ab Initio study of the Co and Ni complexes, vacancies, and pairs in ZnS

Transitional metal impurities in wide band-gap semiconductors are excellent platforms to study doped materials' magnetic properties for optoelectronics, quantum information, and spintronic applications. This study focuses on cobalt (Co) and nickel (Ni) substitutional impurities in zinc-sulfide (ZnS). We first calculate the electronic structures and density of states for substitutional Co and Ni, as well as Co-vacancy, Ni-vacancy, Co-Co pairs, Ni-Ni pairs, and Co-Ni pairs. We also compute the formation energies in different charged states. For the transition metal pairs, we also compute the exchange energy between the ferromagnetic and antiferromagnetic configurations and report the dependence of this energy on the pair separation in the ZnS host. Finally, we add the Hubbard U corrections and report the change in the FM-AFM ground state as a function of the strength of the U parameter.