Based on the optimized crystal structure, 18 superpositions were generated using PHONOPY, and then
thermodynamic properties were calculated. Figure 7 (a) shows the results for monoclinic phase including entropy,
enthalpy, and free energy with temperature from 0 to 1000 K. Figure 7 (b) shows the temperature dependence of
specific heat capacity at constant volume. The result from CASTEP calculation was also included. The comparison
with experiment [9] and simulation [12] in literature shows an excellent agreement.