In Fig. , we present the absolute differences of vibrational frequencies with respect to reference values calculated using pcseg-3 for acetone in water and pcseg-4 for acetone in vacuum. It is clear that the errors are very large when using pcseg-1, especially for the highfrequency modes. Using instead pcseg-2 substantially reduces the errors for both acetone in vacuum and acetone in water, leading us to conclude that pcseg-2 is an adequate choice when also taking into consideration the computational cost. For pcseg-2, the average error ± standard deviation (maximum value) across all normal modes is 3.58 ± 3.36 (14.47) cm -1