As shown in Fig. , a linear regression perfectly fits the curve of 𝑌~1 𝑇 with a coefficient of determination R 2 =1 from M.P. to the critical temperature (Tc). Here, it should be noted that the maximum value of R 2 is 1. R 2 =1 indicates that the fitting is perfect. As R 2 deviates from 1, the smaller the fitting, the worse. Since the coefficient R in the figures duplicates the gas constant, D 2 will be used instead of R 2 in the context. Therefore, Eq. 2 may be altered by Eq. 4.