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Cygan, Randall T.
Greathouse, Jeffery A.; Teich-Mcgoldrick, Stephanie; Jove-Colon, Carlos F.; Cygan, Randall T.
Greathouse, Jeffery A.; Cygan, Randall T.
Cygan, Randall T.
Greathouse, Jeffery A.; Teich-Mcgoldrick, Stephanie; Cygan, Randall T.; Jove-Colon, Carlos F.
Cygan, Randall T.; Altman, Susan J.
Greathouse, Jeffery A.; Teich-Mcgoldrick, Stephanie; Zeitler, Todd Z.; Cygan, Randall T.
Environmental Science and Technology
Criscenti, Louise; Cygan, Randall T.
Proposed carbon dioxide sequestration scenarios in sedimentary reservoirs require investigation into the interactions between supercritical carbon dioxide, brines, and the mineral phases found in the basin and overlying caprock. Molecular simulations can help to understand the partitioning of metal cations between aqueous solutions and supercritical carbon dioxide where limited experimental data exist. In this effort, we used classical molecular dynamics simulations to compare the solvation of alkali and alkaline-earth metal cations in water and liquid CO2 at 300 K by combining a flexible simple point charge model for water and an accurate flexible force field for CO2. Solvation energies for these cations are larger in water than in carbon dioxide, suggesting that they will partition preferentially into water. In both aqueous and CO2 solutions, the solvation energies decrease with cation size and increase with cation charge. However, changes in solvation energy with ionic radii are smaller in CO2 than in water suggesting that the partitioning of cations into CO2 will increase with ion size. Simulations of the interface between aqueous solution and supercritical CO2 support this suggestion in that some large cations (e.g., Cs + and K+) partition into the CO2 phase, often with a partial solvation sphere of water molecules. © 2012 American Chemical Society.
Greathouse, Jeffery A.; Cygan, Randall T.; Zeitler, Todd Z.
Greathouse, Jeffery A.; Cygan, Randall T.; Teich-Mcgoldrick, Stephanie; Nenoff, Tina M.
Zavadil, Kevin R.; Spoerke, Erik D.; Delnick, Frank M.; Anderson, Travis M.; Apblett, Christopher A.; Cygan, Randall T.; Ihlefeld, Jon F.
Muller, Richard P.; Cygan, Randall T.; Deng, Jie; Frischknecht, Amalie L.; Hewson, John C.; Moffat, Harry K.; Tenney, Craig M.; Schultz, Peter A.; Wagner, Gregory J.
Cygan, Randall T.; Greathouse, Jeffery A.; Thurmer, Konrad; Gordon, Margaret
Zeitler, Todd Z.; Greathouse, Jeffery A.; Cygan, Randall T.
Greathouse, Jeffery A.; Cygan, Randall T.; Jove-Colon, Carlos F.
Cygan, Randall T.; Greathouse, Jeffery A.; Jove-Colon, Carlos F.
Cygan, Randall T.; Greathouse, Jeffery A.; Jove-Colon, Carlos F.
Spoerke, Erik D.; Hudak, Nicholas S.; Rodriguez, Mark A.; Cygan, Randall T.; Boyle, Timothy; Wheeler, Jill S.; Zarick, Holly F.; Ingersoll, David; Delnick, Frank M.
Zavadil, Kevin R.; Apblett, Christopher A.; Delnick, Frank M.; Spoerke, Erik D.; Cygan, Randall T.; Anderson, Travis M.
Journal of Physical Chemistry C
Greathouse, Jeffery A.; Cygan, Randall T.
Greathouse, Jeffery A.; Cygan, Randall T.; Teich-Mcgoldrick, Stephanie; Nenoff, Tina M.
Greathouse, Jeffery A.; Cygan, Randall T.; Zeitler, Todd Z.
Journal of physical chemistry C
Greathouse, Jeffery A.; Cygan, Randall T.
Physical Chemistry Chemical Physics
Zeitler, Todd Z.; Greathouse, Jeffery A.; Cygan, Randall T.
While performing molecular dynamics simulations of water or aqueous solutions in a slab geometry, such as at mineral surfaces, it is important to match bulk water density in the diffuse region of the model system with that expected for the appropriate experimental conditions. Typically, a slab geometry represents parallel surfaces with a variable region of confined water (this region can range in size from a few Ångstroms to many tens of Ångstroms). While constant-pressure simulations usually result in appropriate density values in the bulk diffuse region removed from either surface, constant-volume simulations have also been widely used, sometimes without careful consideration of the method for determining water content. Simulations using two thermodynamic ensembles as well as two methods for calculating the water-accessible volume have been investigated for two distinct silicate surfaces - hydrophilic cristobalite (111) and hydrophobic pyrophyllite (001). In cases where NPT simulations are not feasible, a simple geometry-based treatment of the accessible volume can be sufficient to replicate bulk water density far from the surface. However, the use of the Connolly method can be more appropriate in cases where a surface is less well-defined. Specific water-surface interactions (e.g., hydrophobic repulsion) also play a role in determining water content in a confined water simulation. While reported here for planar surfaces, these results can be extended to an interface with any solvent, or to other types of surfaces and geometries. © the Owner Societies 2012.
Physical Chemistry Chemical Physics
Zeitler, Todd Z.; Greathouse, Jeffery A.; Cygan, Randall T.
While performing molecular dynamics simulations of water or aqueous solutions in a slab geometry, such as at mineral surfaces, it is important to match bulk water density in the diffuse region of the model system with that expected for the appropriate experimental conditions. Typically, a slab geometry represents parallel surfaces with a variable region of confined water (this region can range in size from a few Ångstroms to many tens of Ångstroms). While constant-pressure simulations usually result in appropriate density values in the bulk diffuse region removed from either surface, constant-volume simulations have also been widely used, sometimes without careful consideration of the method for determining water content. Simulations using two thermodynamic ensembles as well as two methods for calculating the water-accessible volume have been investigated for two distinct silicate surfaces - hydrophilic cristobalite (111) and hydrophobic pyrophyllite (001). In cases where NPT simulations are not feasible, a simple geometry-based treatment of the accessible volume can be sufficient to replicate bulk water density far from the surface. However, the use of the Connolly method can be more appropriate in cases where a surface is less well-defined. Specific water-surface interactions (e.g., hydrophobic repulsion) also play a role in determining water content in a confined water simulation. While reported here for planar surfaces, these results can be extended to an interface with any solvent, or to other types of surfaces and geometries. © the Owner Societies 2012.
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