where 𝜌 𝐹𝐶𝑊𝑇 (𝛥𝐸 𝑖𝑗 ) is the Franck-Condon factor and temperature-weighted density of states and ℏ is the reduced Planck's constant. On expanding the first term in Eq. 8, we get The average fluctuation of the dihedral angles 〈Δ𝜃 𝑘 〉 = 0, while 〈Δ𝜃 𝑘 2 〉 which signifies the spread of the dihedral angle fluctuation, can be derived by 〈Δ𝜃 𝑘 2 〉 = 𝑘 𝐵 𝑇/𝐾 𝜃 𝑘 from equipartition principle (considering the torsional oscillations as classical); 3 𝐾 𝜃 𝑘 is the elasticity constant of torsional motion about the bond between monomer 𝑘 and 𝑘 + 1 and 𝑘 𝐵 is the Boltzmann constant. In addition, we consider that the fluctuations of the dihedral angles are uncorrelated, i.e., we consider a set of Einstein oscillators.