where 𝐴 𝑚 is the 𝑚-th expansion coefficient while 𝜃 is represented in radian units. We find that the median root mean square error (𝑅𝑀𝑆𝐸) of the fitting for the set of monomer pairs is 2 meV (Fig. shows a typical fitting of this quality and Fig. in the supporting information shows the distribution of RMSE). There are 12 monomer pairs out of 153 with a relatively large RMSE in the range of 6-10 meV, which is probably still satisfactory and could be improved systematically by extending the cosine series (the fittings are shown in Fig. of the SI).