For large systems, numerous low vibrational frequency modes appear, which potentially leads to a large error in the calculated vibrational entropy contribution. We applied the quasiharmonic approximation by Grimme to correct vibrational frequencies below 100 cm -1 . In the quasi-harmonic approximation, these vibrations are treated as free rotors when calculating the vibrational entropy contribution. Unless otherwise stated, all calculations of free energies are presented at 298.15 K and reference pressure of 1 atm.