Figure 5.

Spin configurations and possible AF state

(A) Left panel: spin configurations of Ni 3d⁸ in a square-planar environment. High-spin state with S = 1 and low-spin state with S = 0. Right panel: crystal field splitting on Nd.

(B) Calculated probabilities for the three-electron S = 1/2, two-electron S = 0 and 1 states as a function of Hund’s coupling J_H. Adapted from Wan et al.⁸⁸

(C) Exchange interaction of RNiO₂ calculated by 4t²/U, based on different schemes of theoretical methods DFT, Wannier, and linear response theory, compared with the cuprate exchange interactions that are taken from some experimental results. Adapted from Been et al.¹³⁴

(D) The Hubbard U dependent of exchange coupling parameters.

(E) The estimated T_N. Adapted from Liu et al.¹³⁵