AB-INITIO STUDY OF HYDROGEN-BONDING IN THE PHENOL WATER-SYSTEM

Three hydrogen-bonded minima on the phenol-water, C6H5OH-H2O, Potentia l energy surface were located with 3-21G and 6-31G* basis sets at bot h Hartree-Fock and MP2 levels of theory. MP2 binding energies were com puted using large ''correlation consistent'' basis sets that included extra diffuse functions on all atoms. An estimate of the effect of exp anding the basis set to the triple-zeta level (multiple f functions on carbon and oxygen and multiple d functions on hydrogen) was derived f rom calculations on a related prototype system. The best estimates of the electronic binding energies for the three minima are -7.8, -5.0, a nd -2.0 kcal/mol. The consequences of uncertainties in the geometries and limitations in the level of correlation recovery are analyzed. It is suggested that our best estimates will likely underestimate the com plete basis set, full Cl values by 0.1-0.3 kcal/mol. Vibrational norma l modes were determined for all three minima, including an MP2/6-31G* analysis for the most strongly bound complex. Computational strategie s for larger phenol-water complexes are discussed. (C) 1993 by John Wi ley & Sons, Inc.