Models with Re atoms: (a) single Re configurations; (b) NN Re–Re configurations; (c) NNN Re–Re configurations; (d) Re cluster configurations. S1–S10 denotes ten different single Re atom systems, each system contains one Re atom. The S1′, S3′, and S5′ models are the Re atoms occupying the Ni sites in γ′ phase; A1–A5 denote five different NN Re–Re pair systems, each system contains two Re atoms; B1–B6 denote six different NNN Re–Re pair systems, each system contains two Re atoms; C1–C5 denote five different Re cluster systems, each system contains five Re atoms.