Experimental and theoretical studies of water clusters have greatly advanced in recent years, yet the accurate description of local interactions in water clusters remains difficult using standard methods. Local behaviour is particularly important for non-bulk water environments such as at aqueous interfaces, inside enzyme active sites and filling nanotubes. We apply a new way of evaluating local stabilities in weakly interacting systems using atomic energies that are exactly defined within Bader's quantum theory of atoms in molecules. Changes in atomic energies for interacting molecules can be visually represented as local areas of stabilization and destabilization. We thus demonstrate at the atomic level the strong hydrogen bond cooperativity present in cyclic water clusters, (H2O)n, n=2-5, through increasingly stabilized oxygen and destabilized hydrogen atoms. Evaluation of a set of low lying water hexamer minima (prism, cage, boat 1, boat 2, bag, chair, book 1, book 2) shows the gradual loss of cooperative enhancement as the clusters gain three-dimensional character. Although the net stability of water molecules in these systems may be very similar, their local atomic stabilities can differ largely. This is in part due to the bonding environment of neighbouring water molecules, which is an important tool for predicting local stability and cooperativity. To further explore cooperative hydrogen bonding in water we explore the behaviour of short, one dimensional water chains of 2-5, 7 and 12 waters (often called �water wires�). The influence of chain length and the impact of metal and halide ions on local stability and hydrogen bond cooperativity are evaluated in terms of atomic energies and changing bond critical point values. 

Investigating local stability in water clusters using atomic energies

247th National Meeting (2014)

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