A new feature for the calculation of thermochemical contributions

[IannLiu]

Hi, Tom I recommend a new feature for the calculation of thermochemical contributions.
The qRRHO treatment proposed by Grimme only applies to entropy. Recently, another paper (J. Comput. Chem., 44, 1807 (2023)) proved that using Grimme's scheme to calculate the enthalpy contribution will ensure the internal consistency and improve the quality of Gibbs free energies (ΔGr).

This approach can be easily realized by incorporating a few lines of code. For example:

U_free_rotor = 0.5 * SIConstants.k_b * temp
U_qRRHO = w * U_RROH + (1 - w) * U_free_rotor

where U_RROH is the internal energy from vibrational motion and w is calculated by (line 378 in autode.thermochemistry.igm.py):
w = 1.0 / (1.0 + (omega_0 / freq) ** alpha)