QUANTUM AND STATISTICAL MECHANICAL STUDIES OF LIQUIDS .4. MINIMAL BASIS SET DESCRIPTION OF THE STRUCTURE AND PROPERTIES OF LIQUID WATER

A Monte Carlo simulation of liquid water at 25 °C has been carried out using an intermolecular potential function derived from ab initio molecular orbital calculations with a minimal basis set (STO-3G). Comparisons are made with results for structural and thermodynamic properties from simulations based on potential functions representative of Hartree-Fock level (HF) and configuration interaction (CI) calculations. The quality of the results for the liquid is not enhanced smoothly as the ab initio calculations become more sophisticated. The STO-3G and CI potentials yield similar descriptions of liquid water, while the HF potential predicts too little structure beyond the first solvation shell and too high an energy. The first peak in the oxygen-oxygen radial distribution function is some what too high and displaced to shorter distances with the STO-3G potential than from the experimental or CI results. Nevertheless, the coordination number and energy distribution functions are similar in the simulations with the STO-3G and CI potentials. It is established that reasonable intermolecular potential functions for hydrogen-bonded dimers can be obtained from minimal basis set calculations. © 1979, American Chemical Society. All rights reserved.