Computationally Intensive Research Project

Molecular Computational Studies in Geochemistry and Environmental Chemistry

James R. Rustad,¹ David A. Dixon,² William H. Casey,¹ Kevin M. Rosso,³ Sebastien N. Kerisit,³ Eric J. Bylaska,³ Gregory K. Schenter,³ Marat Valiev,³ Michel Dupuis,³ John H. Weare⁴

¹University of California-Davis, ²University of Alabama-Tuscaloosa, ³Pacific Northwest National Laboratory, ⁴University of California-San Diego

FY07 Allocation - 400,000

Abstract

This project is focused on prediction of reaction rates, mechanisms, and associated isotopic fractionation factors of key processes in low-temperature geochemistry. Such processes can play a key role in the environmental fate of contaminants such as those present in the subsurface at DOE nuclear production facilities. This proposal combines several geochemical research threads including electron transfer, proton transfer, and ligand exchange reactions in interfacial geochemistry. In each area, the latest theory and simulation methods are closely coupled to recent experiments capable of assessing mechanistic detail for elementary geochemical reactions in model systems. During the last decade, important methodological advances in computational chemistry at the electronic structure and molecular dynamics levels have allowed progress to be made in understanding rates and mechanisms of chemical reactions in complex media, such as those occurring in aqueous solutions. These computational methods promise the ability to calculate rates for real geochemical reactions using the tools of quantum chemistry, molecular dynamics, and computational kinetics. The rates reflect the accessibility of the reactant site to water molecules and the details of bonding, such as charges and the Brønsted acidities of particular oxygen atoms in the reacting molecule and the energies of electrons in a reaction step. These studies will be combined to assess the extent to which reactivity in geochemical systems can be reduced to knowledge of structure.