Structures and thermodynamic properties of (C2H6)n (n = 2–8) by M06-2X and DFT-D theory: Implications for Titan’s atmospheric chemistry

The mPW2PLYP-D, B2PLYP-D and M0N-2X functionals are applied to predict structures and energies of (C2H6)n with n ⩽ 8. A comparison between DFT, DFT-D and CCSD(T) results shows that DFT-D delivers accurate binding energies, while M06-2X performs at a reduced cost relative to DFT-D. Incremental M06-2X clustering free energies for (C2H6)n reveal magic number effects for n = 6–7, and these become increasingly more exergonic as the temperature shifts below 70 K. Results from M06-2X calculations give an accurate and computationally affordable description of interactions between C2H6 molecules, and can be applied to predict the stability and abundance of ethane cluster in Titan’s atmosphere.