Phase diagram. Experimental data regard to the phase boundary between γ and α phases (open circle). The green dashed lines are from Ref. [11]. The blue and violet solid lines are the theoretical phase boundary for γ and α phases from Refs. [20] and [31], respectively. The segment I, II, and III are the theoretical lines of present work. Across segment I and III represents an event of first-order phase transition. Across segment II implies that γ-Ce becomes unstable.