Intermolecular interaction potentials of methane and ethylene dimers calculated with the Møller–Plesset, coupled cluster and density functional methods

Intermolecular interaction potentials of methane and ethylene dimers were calculated by the Hartree–Fock, Møller–Plesset, coupled cluster and density functional methods. The CCSD(T) electron correlation energies were close to the MP4(SDTQ) ones. The MP2 and MP3 energies were not largely different from the MP4(SDTQ) ones. On the other hand the CCSD and MP4(SDQ) methods largely underestimated the electron correlation energies. Dispersion interaction was not covered by the density functional methods using the BLYP, BPW91 and B3LYP functionals. These functionals also had defects in the evaluation of the repulsion interactions.