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

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