The recent discovery of superconductivity in doped rare-earth infinite-layer nickelates RNiO$_2$, R=Nd, Pr as a new family of unconventional superconductors has inspired extensive research on their intriguing properties. One of the major motivation to explore the nickelate superconductors originated from their similarities with and differences from the cuprate superconductors.

In this talk, I will present our recent investigation of the relevance of Ni/Cu-3d multiplet structure on the hole doped spin states in cuprate and nickelate superconductors via an impurity model incorporating all the 3d orbitals. Further plausible explorations to be conducted will also be discussed.