Water structure and the valence sum rule

GEOC 4

Barry R. Bickmore, barry_bickmore@byu.edu, Department of Geological Sciences, Brigham Young University, P.O. Box 24606, Provo, UT 84602, Kevin M. Rosso, kevin.rosso@pnl.gov, Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99352, I. David Brown, idbrown@mcmaster.ca, Brockhouse Institute for Materials Research, McMaster University, King St. W, Hamilton, ON L8S 4M1, Canada, and Eric J. Bylaska, eric.bylaska@pnl.gov, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352.
Pauling's valence sum rule, as modified over several decades by bond-valence theorists, has now been shown to apply to time-averaged aqueous solution structures. Ab initio molecular dynamics simulations of 64 water molecules and several oxo-species in baths of 30-31 water molecules, using the PBE96 density functional, were subjected to computerized valence analysis. In all cases, the valence sum rule was followed very closely. Simulations of proton-ordered ice structures were used to obtain reasonable cutoff distances for hydrogen bonds, and hydrogen bond types were also evaluated based on recent synchrotron studies. The hydrogen-bonded structure of the water revealed by analysis of these simulations more closely resembles the structures recently inferred from X-ray absorption spectroscopy, and produces excellent radial distribution functions. These results show that valence analysis can be applied to proposed liquid, as well as solid, structures. Furthermore, they have considerable import for models of surface reactivity based on structural parameters.
 

Frontiers in Geochemistry: Commemorating the 25th Anniversary of the ACS-Geochemistry Division
9:00 AM-11:55 AM, Sunday, 10 September 2006 Moscone Center -- Room 262, Oral

Division of Geochemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006