Matt K. Petersen

A bond-order analysis of the mechanism for hydrated proton mobility in liquid water.

Bond-order analysis is introduced to facilitate the study of cooperative many-molecule effects on proton mobility in liquid water, as simulated using the multistate empirical valence-bond methodology. We calculate the temperature dependence for proton mobility and the total effective bond orders in the first two solvation shells surrounding the H(5)O(2) (+) proton-transferring complex. We find that proton-hopping between adjacent water molecules proceeds via this intermediate, but couples to hydrogen-bond dynamics in larger water clusters than previously anticipated. A two-color classification of these hydrogen bonds leads to an extended mechanism for proton mobility.

The properties of ion-water clusters. II. Solvation structures of Na+, Cl−, and H+ clusters as a function of temperature

Ion-water-cluster properties are investigated both through the multistate empirical valence bond potential and a polarizable model. Equilibrium properties of the ion-water clusters H+(H2O)100, Na+(H2O)100, Na+(H2O)20, and Cl-(H2O)17 in the temperature region 100-450 K are explored using a hybrid parallel basin-hopping and tempering algorithm. The effect of the solid-liquid phase transition in both caloric curves and structural distribution functions is investigated. It is found that sodium and chloride ions largely reside on the surface of water clusters below the cluster melting temperature but are solvated into the interior of the cluster above the melting temperature, while the solvated proton was found to have significant propensity to reside on or near the surface in both the liquid- and solid-state clusters.

Modeling condensed-phase chemistry through molecular dynamics simulation

The challenges and problems involved in simulating condensed-phase dynamics, particularly for systems involving cleavage and formation of chemical bonds, are substantial. The authors describe two methods for simulating protonated liquid water and condensed-phase reaction dynamics, in which the commonly used multi-atom empirical force fields are inadequate.