Interactions between water molecules in the vapour and condensed phases

Abstract

A modified version of the Iterative Extended Hückel Molecular Orbital Method is described which gives equilibrium configurations for the isolated H₂O and H₂O₂ molecules in good agreement with experimental data and permits the approximate calculation of intermolecular potential energies in systems of up to eight water molecules in specified relative configurations. Estimates of the water dimer interaction compare favourably with published results of other methods. An estimate of the interaction energy and O–O distance in ice in reasonable agreement with experiment is obtained. Calculations of the relative stability of staggered and eclipsed conformations of water molecules indicate little difference in the internal energy of Ice I and Ice Ic, in agreement with experiment. Calculations on the restricted rotation of a fully coordinated water molecule yield results in fair agreement with observed IR and Raman librational absorptions. The energy of hydrogen bond bending is estimated and found to lie between previous estimates. The effect of near neighbours upon pair interactions is examined and it is found that two-body potentials alone cannot provide a correct description of intermolecular interaction or structure in water.