A very important aspect is that MD simulations with frozen out rotations cannot recover centrifugal effects. Centrifugal expansion is a few orders of magnitude smaller than the anharmonic shift (see Table ) and is negligible in comparison to standard errors of our MD values. Thus, even with allowed rotations the uncertainty of MD prevents its usage for calculation of this particular effect. On the other side, it is mostly dominated by the harmonic potential and therefore is well predicted in the harmonic approximation with a much smaller computational cost. Two additional tests of the proposed computational methods were done using the moderate-size molecular systems (see Figure ), 6,6-dimethyl-1,5-diazabicyclo[3.1.0]hexane (C 6 H 12 N 2 ) and syn-conformer of 6,6'-bis(3-oxadiamantane) (C 26 H 34 O 2 ). Both structures were earlier investigated experimentally by gas electron diffraction (GED). For the latter molecule GED data were supplemented by rotational constants from microwave measurements. Results of our calculations for these two molecules are given in Table . The (B e -B 0 ) values obtained by WS+MD simulations are in reasonable agreement with those from VPT2. The relative deviations are about of the same order of magnitude as for the smaller systems discussed above. Thus, WS+MD can probably be applied to larger and more complicated molecules.