Basic Research Needs for Geosciences - Energetics Meetings and ...

PRIORITY RESEARCH DIRECTION:MINERAL-WATER INTERFACE COMPLEXITY AND DYNAMICSbeing able to simulate thousands of atoms over sufficiently long time scales to determine timeaveragedmineral-water interface stabilities. Continual improvement in the scalability andimplementation of such methods across emerging petascale computing resources could allow atleast a factor of ten increase in both numbers of atoms and simulation time scales over currentcapabilities (see sidebar on Solid-state charge transport at mineral-water interfaces). To makereliable kinetic predictions, it is critical to not only be able to provide good energies, but also tobe able to sample the phase space of the system well enough to be able to predict consistentreaction paths, mechanisms, and rate constants along with the entropy of the system. Whereasthis can be accomplished for single molecules, it is far more difficult to do for solutions, surfacesand interfaces. Progress is being made in this area, but substantial advances are needed for theprediction of reliable parameters for use in higher scale models.Specifically for radionuclides, generally applicable electronic structure methods for the reliableprediction of the properties of molecular systems and materials with active f electrons need to bedeveloped. These systems with actinides require relativistic treatments because of the highatomic number. New theoretical approaches, including advances in Density Functional Theory todeal with the strongly correlated electron problem, techniques to deal with the multiplet problem,and new methods to predict important properties of materials and chemicals with known errorlimits, need to be developed. These techniques need to be applicable to heavy elements insolution, in the solid state, and at surfaces, and need to be useful for predictions to chemicalaccuracy of the thermodynamics and kinetic processes for complex interfacial systems.SCIENTIFIC CHALLENGESFundamental challenges involve the ability to:1. Translate a molecular-scale description of complex mineral surfaces to thermodynamicquantities for the purpose of linking with macroscopic models2. Follow interfacial reactions in real time to separate out the roles of kinetic andthermodynamic phenomena3. Understand the mechanisms by which minerals grow or dissolve, and how these mechanismsdynamically couple to changes at the interface4. Understand the interrelationships between hydration structure and mineral reactivity at thesame level of detail with which we currently understand aqueous ion reactivity5. Observe elementary oxidation state changes of mineral surfaces and reactants, and determinethe kinetics of associated electron transfer reactions6. Isolate element-specific aspects of interfacial reactions with high spatial and temporalresolutionA key goal will be to understand how these molecular-level aspects of interfacial phenomenadepend on temperature and solution composition, and how they are related to macroscopicobservables so that the results can be connected to larger-scale experimental and theoreticalcharacterizations. It will be necessary to apply these objectives to conditions beyond highlyidealized mineral-water interfaces near equilibrium to appreciate the role of complexity underreactive conditions where the interfacial composition and structure may be dynamically changingwith time.Basic Research Needs for Geosciences: Facilitating 21 st Century Energy Systems 111