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I would like to know whether the normal mode of vibration of the reactant should be deleted when calculating $\Delta ZPE$ and $\delta G_{\text{corr}}(T)$, where $\Delta ZPE$ is the zero-point energy difference between the minimum and the TS and $\delta G_{\text{corr}}(T)$ is the difference between the thermal corrections of the minimum and the TS. In the TS with $N$ atoms there are $3N-7$ degrees of freedom. Should I use the same number of vibration in case of the reactant, as well?

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  • $\begingroup$ Are you talking about zero-point correcting a TS? Related: chemistry.stackexchange.com/questions/6610/… $\endgroup$ – LordStryker May 18 '17 at 17:40
  • $\begingroup$ Yes. What is your opinion about leaving the vibration coordinate conforming to the imaginary mode? $\endgroup$ – Roloka May 19 '17 at 6:15
  • $\begingroup$ Include it in the zpve correction. This is what is commonly done in the literature. $\endgroup$ – LordStryker May 19 '17 at 6:22
  • $\begingroup$ Including it provides a negative free energy of activation, because the reactant and the product are two conformers of n-pentane, thus they are drastically similar, but they have huge ΔZPVE. $\endgroup$ – Roloka May 19 '17 at 7:23
  • $\begingroup$ Other source of errors (applying the harmonic approximation and anharmonic correction) cannot occur, all calculations were performed with state-of-art computations within the focal-point approach (e.g. we used geometries close to the CCSD(T)/cc-pVTZ ones, extrapolated ΔHF, δMP2, δCCSD, δCCSD(T) terms, based on MP2/cc-pVXZ and CCSD(T)/cc-pVXZ single point calculations up to X=5 and X=4, respectively). The free-energy differences of the conformers are in agreement with the values from the litterature. $\endgroup$ – Roloka May 19 '17 at 7:23

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