(a) Pressure-dependent unit volume of MoS₂ in both 2H_c and 2H_a phases. (b) Pressure-dependent relative Gibbs free energy of 2H_a- and 2H_c-MoS₂ phases. (c) Phase diagram of MoS₂ from 2H_c-to-2H_a as a function of thickness. The solid line is the dividing line.