L † ⟨0|I -1 |0⟩ L, where |0⟩ is the ground vibrational state, and L are the angular momentum operator. To quantify the performance of the methods, we have computed Pearson correlation coefficients ρ for the observed normalized rotational constant shifts from the MD trajectories and VPT2. The results are summarized in Table . MIITO showed the best performance among all of the routines applied, and therefore it was further used as a default procedure for calculation of vibrationally-averaged rotational constants from MD trajectories. The resulting vibrational corrections to rotational constants are listed in Table . As one can see, the MD values correlate quite well with the reference values from the VPT2 model.