Fundamental Studies in Chemistry
Using PSC's Terascale System, University of Pennsylvania scientist Michael Klein and colleagues are carrying out fundamental studies of an important chemical system, the hydroxide ion (OH-) in water. This system has drawn the attention of chemists for years, even centuries, because of high electrical conductivity. In spite of many experimental studies in recent years — including neutron diffraction analyses and spectroscopic studies — there's not settled understanding about what molecular forms of hydroxide occur.
Klein's research team employed a powerful, quantum-theory based simulation technology called Car-Parinello molecular dynamics. They used up to 128 Terascale processors in parallel to simulate varying concentrations of sodium hydroxide and potassium hydroxide solutions. Prior computational studies of the hydroxides excluded the counterions, sodium and hydroxide, due to the added computational difficulty.
Their results, reported in the Journal of American Chemistry, include several important findings. Among them is that the clustered molecular structures of water change dramatically with the presence of hydroxide ions at high concentrations. Another important finding is that the solvation structure of hydroxide varies with concentration. At low concentration, H9O5- is preferred. At high concentrations H9O5- remains, but other structures are also present — H7O4- and H11O6-.
This study, say the researchers, could not have been carried out except for LeMieux. Another paper in progress from these simulations will put forth a detailed atomic-level explanation of the proton-transfer mechanism in this system.