Structure of water clusters computed with the aid of molecular graphics

Abstract

A computer system has been developed with which the equilibrium structures of neutral and protonated clusters of n water molecules can be found using two-body potentials. The novel features of the system are the ability to construct clusters interactively on a graphics display, to manipulate them to find approximate energy minima, to transfer the preliminary structures to a large mainframe computer for optimization, and to return the final structure for display and investigation of its properties. Results are presented for neutral cluster sizes up to n = 21 and for ionized (protonated) clusters around n = 20. The potentials used are based on ab initio Hartree-Fock and CI calculations. Although the calculated structures confirm the stability of rings of five water molecules and dodecahedral structures, (H 2O) 20 is not predicted to be conspicuously stable relative to smaller or larger clusters. On the other hand the ionized cluster H +(H 2O) 21 has a greater binding energy permolecule than its neighbours, in agreement with mass spectroscopic observations.