AB-INITIO AND DENSITY-FUNCTIONAL CALCULATIONS ON ETHYLENE-GLYCOL

A comparative study between a high-level ab initio molecular orbital methods and density functional theory (DFT) employing local and nonlocal density approximations has been performed on 10 equilibrium conformers of ethylene glycol. These 10 structures are separated by relatively small energy differences with the two lowest energy structures forming intramolecular hydrogen bonds. All 10 conformers were optimized, by both methods, using comparable basis sets (double-zeta plus polarization in valence orbitals) including correlation effects, followed by even larger basis set single-point energy calculations. The optimized geometries and the relative energies calculated by the DFT method, when nonlocal and gradient corrections to the exchange-correlation potential (NLGC) were included, are found to be in good agreement with the ab initio results. The effects of the NLGC on the geometries and relative energies with special attentions to hydrogen bonding and the gauche effect are discussed.