“…The curvature scalar of the Ruppeiner geometry is related to the correlation volume of a thermodynamic system, and its divergent point is the critical point of the thermodynamic phase transition. The properties of the thermodynamic geometries of the black hole have been widely studied [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. It has been found that the Ruppeiner thermodynamic geometry of the Reissner–Nordström (RN) black hole is flat [ 37 ].…”