NONBONDING INTERACTION POTENTIAL OF ETHYLENE DIMER OBTAINED FROM ABINITIO MOLECULAR-ORBITAL CALCULATIONS - PREDICTION OF A D(2D) STRUCTURE

Nonbonding interaction potentials of 12 orientations of ethylene dimer were calculated at the MP2/6-311G(2d,2p) level with basis set superposition error correction. The potential of a D2d orientation has a deepest minimum of -1.07 kcal/mol. This orientation agrees with the structure predicted from the analysis of infrared spectra by Ritter and Gruen. The calculated Coulombic interaction between ethylene molecules based on the HF/6-31G level Mulliken charge of the monomer shows that the Coulombic interaction stabilizes this orientation. Evaluation of the basis set effect on the calculated interaction energy using several basis sets up to the 6-311G(2d,3p) basis set shows that the dispersion energy component, which was calculated as the electron correlation energy, significantly depends on the basis set used. Smaller basis sets underestimate the dispersion energy, whereas the repulsive and Coulombic energy component calculated at the HF level is little affected by the basis set used.