A highly correlated ab initio investigation of the temperature-dependent conformational analysis of cycloheptane

The conformational analysis for the cycloheptane molecule has been carried out at the MP2/6-311G(d,p) and MP2/cc-pVDZ levels of theory, for structural parameters and harmonic frequency calculations, and using MP4(SDTQ) and CCSD(T) highly correlated methods for energy difference evaluation, aiming the determination of the temperature-dependent thermodynamic properties. The importance of using a separate treatment of the low frequency vibrational modes for the calculation of relative Gibbs free energy values is discussed and is shown to play a key role to bring the agreement of the theoretical conformational population predictions with the experimental gas phase reported value at 310 K.