2009. "Solvation of Dimethyl Succinate in a Sodium Hydroxide Aqueous Solution. A Computational Study." Journal of Physical Chemistry B 113(18):6473–6477. Abstract Molecular dynamics simulations were carried out to study dimethyl-succinate/water/NaOH solutions. The potential of mean force method is used to determine the transport mechanism of a dimethyl-succinate (a diester) molecule across the aqueous/vapor interface. The computed number density profiles show a strong propensity for the diester molecules to congregate at the interface with the solubility of the diester increasing with increasing NaOH concentration. It is observed that the major contribution to the interfacial solvation free energy minimum is from van der Waals interactions. Thus, even at higher NaOH concentrations, the increasing electrostatic interaction between the diester and ions is not large enough to overcome the Lennard-Jones (LJ) interactions to favor the solvation of diester in bulk solutions. The calculated solvation free energies are found to be -2.6 ~ -3.5 kcal/mol in variant concentrations of NaOH aqueous solutions. These values are in qualitative agreement with the corresponding experimental measurements. The computed surface potential indicates that the contribution of diester molecules to the total surface potential is about 25%, with the major contribution from interfacial water molecules. This work was supported by the US Department of Energy (DOE) Office of Basic Energy Sciences, Chemical Sciences program. Pacific Northwest National Laboratory is operated by Battelle for DOE.
2009. "Computational studies of aqueous interfaces of RbBr salt solutions ." Journal of Chemical Physics 130(12):Article no. 124709. doi:10.1063/1.3096916 Abstract In this paper, we compute the structural factor and corresponding x-ray reflectivity of the aqueous interface of RbBr salt solutions using molecular dynamics techniques and polarizable and non-polarizable potential models. Our computed electron and number densities clearly demonstrate that the polarizable Br- anions are concentrated at the water surface, while the non-polarizable Br- anions are depleted from the surface. This observation contradicts a recently published conclusion that was based on x-ray reflectivity measurements. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.
2009. "Spontaneous activation of CO2 and possible corrosion pathways on the low-index Iron surface Fe(100)." Journal of Physical Chemistry C 113(9):3691-3696. Abstract This work examines fundamental reactions pertaining to the capture, sequestration and storage of CO2 or other contaminants such as H2O, Sox etc, as well as the corrosion mechanism of steels under SC-Co2 conditions. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.
2009. "Computational studies of load-dependent guest dynamics and free energies of inclusion for CO2 in low-density p-tert-butylcalix[4]arene at loadings up to 2:1 ." Journal of Physical Chemistry A 113(14):3369-3374. doi:10.1021/jp808490g Abstract The structure, dynamics, and free energies of absorption of CO2 by a low density structure of Calixarene p-tert-butylalix[4]arene (TBC4) at loadings up to 2:1 CO2:TBC4 have been studied using molecular dynamics simulations. From the computed radial distribution functions, we notice that the 1:1 loading peak shows a single broad peak from the caged CO2 separation. At higher temperature, the peak is only slightly broadened from the 300 K peak and the shoulder around 11 Å is reduced. The radial distribution function of the 2:1 loading shows a prominent sharp peak around 3 Å and a second peak around 4 Å, indicating a dimer center-of-mass separation of 3 Å that is smaller than that of optimized gas-phase dimer. This result suggests that dimer is sufficiently stabilized by the interaction with the TBC4. The relative angle distributions for paired CO2 molecules are flat and do not show a preference for the crossed geometry found in the vacuum dimer at 3 Å. Angular distributions relative to the TBC4 symmetry axis show a preference for alignment tilted relative to the TBC4 axis closer to the plane of the phenyl rings of the TBC4 cage. Translational velocity autocorrelation calculations show a single peak under all conditions studied with very little change with temperature. Rotational velocity autocorrelation calculations show relatively little structure with significant tailing to low frequencies indicating rotation is hindered in the conical TBC4 cavity in the low density structure. The free energy of inclusion for CO2 in this TBC4 structure at 300 and 450 K for various loadings show the inclusion of a single CO2 in the system is favorable at -4.2 kcal/mol at 300 K and -1.5 kcal/mol at 450 K. The fully loaded 1:1 CO2:TBC4 system is slightly less favorable at -3.6 and -1.0 kcal/mol for 300 and 450 K respectively. The first CO2 added beyond 1:1 loading shows a significant drop in absorption energy to -1.8 and +1.5 kcal/mol at 300 and 450 K. These data are consistent with experimental results showing that low-density structures of TBC4 are able to absorb CO2 at loadings greater than 1:1 but retention is lower than for 1:1 loaded systems indicating the energy of inclusion for addition of the CO2 above 1:1 is less favorable. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.
2009. "Investigating hydroxide anion interfacial activity by classical and multi-state empirical valence bond molecular dynamics simulations." Journal of Physical Chemistry A 113(22):6356-6364. Abstract Molecular dynamics simulations were carried out to understand the propensity of the hydroxide anion for the air-water interface. Two classes of molecular models were used, a classical polarizable model, and a polarizable multi-state empirical valence bond (MS-EVB) potential. The latter model was parameterized to reproduce the structures of small hydroxide-water clusters based on proton reaction coordinates. Furthermore, nuclear quantum effects were introduced into the MS-EVB model implicitly by refitting its potential energy function to account for them. The final MS-EVB model showed reasonable agreement with experiment and ab initio molecular dynamics simulations for dynamical and structural properties. The free energy profiles for both the classical and MS-EVB models were mapped out across the air-water interface, and the classical model gave a higher free energy at the interface with respect to bulk. The MS-EVB model gave a hydroxide anion that approached very close to the interface before it had a sharp increase in free energy at the Gibbs dividing surface. This showed a hydroxide anion that was present at the interface, but strongly repelled from its outer edge near the air. This work was supported by the US Department of Energy's Office of Basec Energy Sciences, Chemical Sciences program. Pacific northwest national Laboratory is operated by Battelle for DOE.
2009. "Computational Studies of Structures and Dynamics of 1, 3-Dimethylimidazolim Salt Liquid and their Interfaces Using Polarizable Potential Models ." Journal of Physical Chemistry A 113(10):2127-2135. doi:10.1021/jp809132w Abstract The structures, thermodynamics, dynamical properties of bulk and air/liquid interfaces of three ionic liquids, 1,3-dimethylimidazolium [dmim]+, Cl-, Br-, and I- are studied using molecular dynamics techniques. In bulk melts, the radial distribution functions reveal a significant long-range structural correlation in these ionic liquids. From the angular distribution analysis, the imidazolium rings are found to lie parallel to each other at short distances, consistent with the structures observed in the crystal state. The single-ion dynamics are studied via mean-square-displacements, velocity and orientational correlation functions. The diffusion coefficients and reorientational times are found to be much smaller than H2O. We also observe that anion size plays an important role in the dynamics of ionic liquids. The computed density profiles of the ionic liquid/vapor interface exhibit oscillatory behavior, indicative of surface layering at the interface. Further analysis reveals that the [dmim]+ ions show preferred orientation at the interface with the ring parallel to the surface and methyl group attached to the ring pointing into the vapor phase. The computed surface tensions indicated small differences between these ionic liquids and are inline with recent experimental measurements. The calculated potential drops of these ionic liquids are found to be small and negative. These results could imply that the cation dipoles are likely to orient in the plane that parallel to the surface normal axis. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.
2008. "Recent advances in understanding transfer ions across aqueous interfaces." Chemical Physics Letters 458(1-3):1-5. doi:10.1016/j.cplett.2008.03.097 Abstract Understanding the composition of aqueous interfaces, and the mechanism for ion transport across them is of fundamental importance for biological, environmental, and industrial processes. Molecular dynamics simulations, using the potential of mean force technique serves as a technique to map out the free energy profile across interfaces. In some cases, where the free energy of ion transfer is known experimentally between two phases, the potential of mean force technique can allow validation of the simulation results against experiment for this property. In addition, the inclusion of polarizability in the interaction potential can be of paramount importance for understanding interfacial properties and the ion transfer mechanism in interfacial environments. This review discusses some of the recent studies of ion transport across aqueous interfaces, and gives insights on the ion transport mechanism and why certain interfacial behavior is observed. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
2008. "Molecular Dynamics Study of Ion Transfer and Distribution at the Interface of Water and 1,2-Dichloroethane (Letter)." Journal of Physical Chemistry C 112(3):647-649. doi:10.1021/jp076608c Abstract Molecular dynamics simulations were carried out to study Cl-’s propensity for and its transfer across the H2O-1,2-dichloroethane (DCE) interface, comparing it with the H2O-CCl4 and H2O-vapor interfaces. It was found that, primarily because the DCE molecules had a preferred orientation at the H2O-DCE interface that resulted in unfavorable interactions with Cl-, Cl- was repelled from the H2O-DCE interface. For CCl4, which has a larger Cl- free energy of transfer from H2O than DCE, Cl- had a propensity for the interface, as well as for the H2O-vapor interface. Calculated thermodynamic properties for pure DCE, the H2O-DCE surface tension, and the free energy of Cl- transfer across the H2O-DCE interface agreed very well with experiment. This study shows that a coexisting solvent’s preferred orientation at the interface can be used to control the propensity of a solute for the aqueous interface. This work was supported by the Office of Basic Energy Sciences of the U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
2008. "Dynamics and free energies of CH4 and CO2 in the molecular solid of the p-tert-butylcalix[4]arene." Chemical Physics Letters 453(4-6):123-128. doi:10.1016/j.cplett.2008.01.031 Abstract The dynamics of the guest molecules CO2 and CH4 in p-tert-butylalix[4]arene (TBC4) motion was studied from 100 K to 400 K using the velocity autocorrelation approach. The rattling motion of the CH4 guest molecules exhibit an increase in the Einstein frequency with increasing temperature as has been observed experimentally and in simulations for some rare gas clathrate systems. The CH4 molecule shows an increase from 75 cm-1 at 100 K to 91 cm-1 at 400 K. The CO2 rattling motion exhibits a single peak and less temperature dependence going from 76 cm-1 at 100 K to 72 cm-1 at 400 K. The rotational spectra for CO2 exhibit two peaks at 100 K with the higher frequency peak shifting to lower frequency with increasing temperature. The computed rotational Einstein frequencies go from 86 cm-1 at 100 K to 71 cm-1 at 400 K. The temperature dependent Gibbs absorption free energies of the guest molecules CO2 and CH4 in TBC4 have also been studied at 1 bar using thermodynamic integration from 10 K to 400 K. As expected, the simulated absorption free energy for CO2 is greater at all temperatures than for CH4. At 10 K, the simulated values of -11.4 kcal/mol and -8.4 kcal/mol for CO2 and CH4, respectively, while at 300 K the values are -5.4 kcal/mol and -4.4 kcal/mol. This work was performed at the Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE.
2008. "Computational studies of liquid water and diluted water in carbon tetrachloride." Journal of Physical Chemistry A 112(8):1694-1700. doi:10.1021/jp711092v Abstract Molecular dynamics simulations were carried out to study solvent effects on the energetic and dynamical properties of water molecules in liquid water and in carbon tetrachloride (CCl4). In these studies, the free energy profiles or potentials of mean force (PMF) for water dimers in both solvents were computed. The computed PMF results showed a stable minimum near 3 Å for the O-O separation, with a minimum free energy of about -2.8 kcal/mol in CCl4, as compared to a value of -0.5 kcal/mol in liquid water. The difference in free energy in water as compared to CCl4 was expected, and is the result of competition from surrounding water molecules, that are capable of forming hydrogen bonds) in the liquid water. This capability is absent in the diluted water found in CCl4. We found that the rotational motions were non-isotropic, with the out-of plane vector correlation times in water/D2O varying from 5.6/5.8 ps at 250 K to 0.57/0.56 ps at 350 K and the corresponding OH/OD bond vectors varying from 6.5/7.7 ps to 0.75/0.75 ps. The results compare reasonably well to the available NMR experimental and computer simulation data on the same system (Farrar and Skinner et al. JACS 2001, 123, 8047). For diluted water in CCl4, we found the computed rotational correlation times also were non-isotropic and much longer than the corresponding NMR experimental values at the same concentration (Farrar et al. J. Phys. Chem. A 2007, 111, 6146). Upon analyzing the water hydrogen bonding patterns as a function of water concentrations, we conclude that the differences in the rotational correlation times mainly result from the formation of water hydrogen-bonding networks as the water concentration is increased in liquid CCl4. In addition, we found the rotational correlation times to be substantially faster in liquid CCl4 than in liquid water. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.
2007. "Segregation of salt ions at amorphous solid and liquid surfaces." In Physics and Chemistry of Ice: Proceedings of the 11th International Conference on the Physics and Chemistry of Ice, vol. 311, ed. W. Kuhs, pp. 217-224. RSC Publishing, London, United Kingdom. Abstract Traditionally, the surfaces of aqueous electrolytes are described as inactive and practically devoid of ions [1, 2]. Indeed, this has turned out to be true for non - polarizable ions, as alkali cations and small anions, as fluoride as well. However, due to polarization interactions singly charged anions, with the heavy halides as particular examples, exhibit a propensity for the water / air (vacuum) interface. This was first suggested in order to rationalize the occurrence of chemical reactions on aqueous interfaces, sea - salt particles, ocean surfaces etc. This initiated MD calculations using polarizable potentials. They suggest that highly polarisable anions can indeed be preferentially adsorbed at the outermost liquid layer. In this description, the ions are polarized by the anisotropy of the interface, creating an induced dipole that is stronger than in the bulk. The interaction between the polarized ions and the surrounding water molecules compensates for the reduced solvation available at the surface. This has triggered a number of laboratory studies, applying mainly non - linear optical probes. Battelle operates Pacific Northwest National Laboratory for the US Department of Energy.
2007. "The Effect of Polarizability for the Understanding the Molecular Structure of Aqueous Interfaces." Journal of Chemical Theory and Computation 3(6):2002-2010. doi:10.1021/ct700098z Abstract A review is presented on recent progress of the application of molecular dynamics simulation methods with the inclusion of polarizability for the understanding of aqueous interfaces. Comparisons among a variety of models, including Car-Parinello simulations, for the modeling of neat air-water interfaces are given. These results are used to describe the effect of polarizability on modeling the microscopic structure of the neat air-water interface, including comparisons with recent spectroscopic studies. Also, the understanding of the contribution of polarization to the electrostatic potential across the air-water interface is elucidated. Finally, the importance of polarizability for understanding anion transfer across an organic-water interface is shown. This work was performed at Pacific Northwest National Laboratory (PNNL) under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. PNNL is operated by Battelle.
2007. "Molecular Mechanism of Transporting a Polarizable Iodide Anion Across the Water-CCl4 Liquid/Liquid Interface ." Journal of Chemical Physics 126(13):, doi:10.1063/1.2717164 Abstract The result of transferring a polarizable iodide anion across the H2O-CCl4 liquid/liquid interface was investigated. The computed transfer free energy profile or potential of mean force exhibits a minimum near the Gibbs dividing surface, and its characteristics are similar to those of found in a corresponding water vapor/liquid interface study involving a smaller minimum free energy. Molecular dynamics simulations also were carried out to compare the concentrations of NaCl, NaBr, and NaI at H2O-vapor and H2O-CCl4 interfaces. While the concentration of bromide and iodide ions were lower at the H2O-CCl4 interface when compared to the H2O-vapor interface, the chloride ion concentrations were similar at both interfaces. Analysis of the solvation structures of iodide and chloride ions revealed that the more polarizable iodide ion was less solvated than the chloride ion at the interface. This characteristic brought the iodide ion in greater contact with CCl4 than the chloride ion, resulting in repulsive interactions with CCl4, which reduced its propensity for the interface. This work was performed at the Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE. The DOE Division of Chemical Sciences and the Scientific Computing Staff, Office of Science provided computer resources at the National Energy Research Supercomputer Center (Berkeley, California) that supported this research.
2007. "Hydroxyl radical transfer between interface and bulk from transition path sampling ." Chemical Physics Letters 444(1-3):66-70. doi:10.1016/j.cplett.2007.06.121 Abstract The transition path sampling technique was used to determine trajectories connecting the interface and bulk for the transfer of a hydroxyl radical from the air-water interface to the water bulk. The trajectories were used to calculate the rate of transfer for the process. In addition, transition state and Grote-Hynes theories were used to calculate the rate of transfer. It was found that transition state theory significantly overestimated the rate of transfer, while the Grote-Hynes theory estimated a transmission coefficient that was fairly close to that from transition path sampling. Analysis of transition states found that a majority of them were not at the free energy barrier from the potential of mean force, but shifted towards the vapor phase. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
2007. "Molecular Dynamics Simulations of the Solution-Air Interface of Aqueous Sodium Nitrate." Journal of Physical Chemistry A 111(16):3091-3098. doi:10.1021/jp0683972 Abstract Molecular dynamics simulations have been used to investigate the behavior of aqueous sodium nitrate in interfacial environments. Polarizable potentials for the water molecules and the nitrate ion in solution were employed. Calculated surface tension data at several concentrations are in good agreement with measured surface tension data. The surface potential of NaNO3 solutions at two concentrations also compare favorably with experimental measurements. Density profiles suggest that NO3 - resides primarily below the surface of the solutions over a wide range of concentrations. When the nitrate anions approach the surface of the solution, they are significantly undercoordinated compared to in the bulk, and this may be important for reactions where solvent cage effects play a role, such as photochemical processes. Surface water orientation is perturbed by the presence of nitrate ions, and this has implications for experimental studies that probe interfacial water orientation. Nitrate ions near the surface also have a preferred orientation that places the oxygen atoms in the plane of the interface. The availability of NO3 - for reaction at the surface of aerosols in the atmosphere is discussed. The work at Pacific Northwest National Laboratory was performed under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. Pacific Northwest National Laboratory is operated by Battelle for the Department of Energy.
2007. "Free energies of CO2/H-2 capture by p-tert-butylcalix[4]arene. A molecular dynamics study." Journal of Chemical Physics 127(10):Art. No. 104702. Abstract The interactions of CO2/H2 with p-tert-butylcalix[4]arene (TBC4) were studied using potential of mean force (PMF) and free energy perturbation approaches. The computed PMFs for the interaction of CO2/H2 with a single TBC4 molecule establish that the interaction of CO2 with the open end of the cage structure is attractive while interaction with H2 is not. Free energy perturbation calculations were performed for the same two guest molecules with a pair of facing TBC4 molecules used as a representative model as found in the TBC4 molecular solid. At low temperature both CO2/H2 have favorable interactions with the TBC4 pair with the CO2 interaction considerably larger. These results are in agreement with recent experimental data showing considerable CO2 uptake by TBC4 at moderate pressures. This work was performed at the Pacific Northwest National Laboratory (PNNL) and was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy (DOE). PNNL is operated by Battelle for the DOE.
2007. "Segregation of inorganic ions at surfaces of polar nonaqueous liquids." Chemphyschem 8(10):1457-1463. Abstract We present a short review of recent computational and experimental studies of surfaces of inorganic salt solutions with polar non-aqueous solvents. These investigations complement our knowledge about aqueous interfaces, showing that liquids such as formamide, liquid ammonia, or ethylene glycol can also surface segregate large polarizable anions like iodide, albeit less efficiently than water. For liquids, the surface of which is plagued with hydrophobic groups (such as methanol), the surface ion effect all but disappears. Based on the present data, a general picture of inorganic ion solvation at the solution/vapor interface of polar liquids is outlined. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.
2006. "Simulated Surface Potentials at the Vapor-Water Interface for the KCl Aqueous Electrolyte Solution." Journal of Chemical Physics 125(2):NIL_312-NIL_315 . doi:10.1063/1.2218840 Abstract Classical molecular dynamics simulations with polarizable potential models were carried out to quantitatively determine the effects of KCl salt concentrations on the electrostatic surface potentials of the vapor-liquid interface of water. To the best of our knowledge, the present work is the first calculation of the aqueous electrolyte surface potentials. Results showed that increased salt concentration enhanced the electrostatic surface potentials, in agreement with the corresponding experimental measurements. Furthermore, the decomposition of the potential drop into static charges and induced dipoles showed a very strong effect on the potential drop (an increase of ~1V per 1M) due to the double layers formed by KCl. However, this was mostly negated by the negative contribution from induced dipoles, resulting in a relatively small overall increase (~0.05V per 1M) in potential drop with increased salt concentration. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy. The funding of the Center for Biomolecules and Complex Molecular Systems is provided by the Ministry of Education of the Czech Republic under the project number LC512. The work performed at the Institute of Organic Chemistry and Biochemistry of the Academy of Sciences of the Czech Republic was a part of the research project Z40550506 and via the NSF-funded Environmental Molecular Science Institute (grants CHE 0431512 and 0209719) is gratefully acknowledged.
2006. "Distribution, structure, and dynamics of cesium and iodide ions at the H2O-CCl4 and H2O-vapor interfaces." Journal of Physical Chemistry B 110(13):6824-6831. doi:10.1021/jp055427c Abstract Molecular dynamics simulations utilizing many-body potentials of H2O-CCl4 and H2O-vapor interfaces were carried out at different cesium and iodide ion concentrations to compare ion distribution, interfacial orientational and structural properties, and dynamics. It was found that cesium was repelled by both interfaces, and iodide was active at both interfaces, but to a much greater degree at the H2O-vapor interface. At the interface, the iodide dipole was strongly induced oriented perpendicular to the interface for both systems, leading to stronger hydrogen bonds with water. For the H2O-CCl4 interface, though, there was a compensation between these strong hydrogen bonds and short to moderate ranged repulsion between iodide and CCl4. Hydrogen bond distance and angular distributions showed weaker water-water hydrogen bonds at both interfaces, but generally stronger water-iodide hydrogen bonds. Both translational and rotational dynamics of water were faster at the interface, while for CCl4, its translational dynamics was slower, but rotational dynamics faster at the interface. For many of the studied systems and species, translational diffusion was found to be anisotropic at both interfacial and bulk regions. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy under contract DE-AC05-76RL01830.
2006. "Computational observation of enhanced solvation of the hydroxyl radical with increased NaCl concentration." Journal of Physical Chemistry B 110(18):8917-8920. doi:10.1021/jp061221f Abstract Classical molecular dynamics simulations with many-body potentials were carried out to quantitatively determine the effect of NaCl salt concentration on the aqueous solvation and surface concentration of hydroxyl radicals. The potential of mean force technique was used to track the incremental free energy of the hydroxyl radical from the vapor, crossing the air-water interface into the aqueous bulk. Results showed increased NaCl salt concentration significantly enhanced hydroxyl radical solvation, which should significantly increase its accommodation on water droplets. This has been experimentally observed for ozone aqueous accommodation with increased NaI concentration, but to our knowledge, no experimental study has probed this for hydroxyl radicals. The origin for this effect was found to be very favorable hydroxyl radical-chloride ion interactions, being stronger than for water-chloride. This work was performed at Pacific Northwest National Laboratory (PNNL) under the auspices of the Division of Chemical Sciences, Office of Basic Energy Sciences, U.S. Department of Energy. Battelle operates PNNL for the Department of Energy.
2006. "Surface segregation of dissolved salt ions." Journal of Physical Chemistry B 110(24):11971-11976. doi:10.1021/jp061437h Abstract Surface segregation of iodide, but not of fluoride or cesium ions, is observed by a combination of metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) of amorphous solid water exposed to CsI or CsF vapor. The same surface ionic behavior is also derived from molecular dynamics (MD) simulations of the corresponding aqueous salt solutions. The MIES results provide first direct evidence for the suggested presence of heavier halides (iodide, bromide, and to a lesser extent chloride) at aqueous surfaces, and confirm the structural similarity between the amorphous solid and the corresponding liquid. In contrast, no appreciable surface segregation of ions is observed in methanol, neither in the experiment nor in the simulation, which points to the remarkable surface properties of water among polar solvents. The propensity of heavier halides for the air/solution interface has important implications for heterogeneous chemical processes, particularly on aqueous aerosols in the atmosphere. This work was supported by the Office of Basic Energy Sciences of the Department of Energy, in part by the Chemical Sciences program and in part by the Engineering and Geosciences Division. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy under contract DE-AC05-76RL01830.
2006. "Electronic Structure, Statistical Mechanical Simulations, and EXAFS Spectroscopy of Aqueous Potassium." Theoretical Chemistry Accounts 115(2-3):86-99. doi:10.1007/s00214-005-0054-4 Abstract We investigate the solvation structure of aqueous potassium ions, using a combination of electronic structure calculations, statistical mechanical simulations with a derived polarizable empirical potential and experimental measurement of the Extended X-ray Absorption Fine Structure (EXAFS) spectra. The potassium K-edge (at 3608 eV) EXAFS spectra were acquired on the bending magnet of sector 20 at the Advanced Photon source, at ambient conditions and for the concentrations of 1m and 4m KCl. We focus on the coordination distances and the degree of disorder of the first hydration shell as determined by electronic structure calculations, molecular dynamics simulations and experimental measurement. Finally, we characterize the changes of the structure in the first hydration shell with increasing temperature as predicted by molecular simulation.
2006. "Molecular mechanisms of hydrogen loaded B-hydroquinone clathrate." Journal of Physical Chemistry B 110(35):17291-17295. doi:10.1021/jp062691c S1520-6106(06)02691-5 Abstract Molecular dynamics simulations are used to investigate the molecular interactions of hydrogen loaded beta-hydroquinone clathrate. It is found that at lower temperatures, higher loadings are more stable, whereas, at higher temperatures, lower loadings are more stable. This trend can be understood based on the interactions in the system. For loadings greater than one, the repulsive forces between the guest molecules shove each other towards the attractive forces between the guest and host molecules leading to a stabilized minimum energy configuration at low temperatures. At higher temperatures greater displacements take the system away from the shallow energy minimum and the trend reverses. The asymmetries of the clathrate cage structure are due to the presence of the attractive forces at loadings greater than one that lead to confined states. The nature of the cavity structure is nearly spherical for a loading of one, leads to preferential occupation near the hydroxyl ring crowns of the cavity with a loading of two, and at higher loadings, leads to occupation of the interstitial sites (the hydroxyl rings) between cages by a single H2 molecule with the remaining molecules occupying the equatorial plane of the cavity. At higher temperatures, the cavity is more uniformly occupied for all loadings, where the occupation of the interstitial positions of the cavities leads to facile diffusion. ACKNOWLEDGEMENT This work was partially supported by NIDO (Japan), LDRD (PNNL), EERE U.S. Department of Energy, and by OBES, U.S. DOE. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy
2006. "On NO3-H2O interactions in aqueous solutions and at interfaces." Journal of Chemical Physics 124(6):066101 (3). doi:10:1063/1.2171375 Abstract Constrained molecular dynamics technique was employed to investigate the transport of a nitrate ion across the water liquid/vapor interface. We developed the nitrate ion-water polarizable potential capable of describing well the solvation properties of the hydrated nitrate ion. The computed free energy profile for the transfer of the nitrate ion across the air/water interface increases monotonically as the nitrate ion approaches the Gibbs dividing surface from the bulk liquid side. The computed density profiles of 1M KNO3 salt solution slab indicate that the nitrate and potassium ions are both found below the aqueous interface. Upon analyzing the results, we can conclude that the probability of finding the nitrate anion at the aqueous interface is quite small.
2006. "Molecular simulation analysis and X-ray absorption measurement of Ca2+, K+, and Cl- ions in solution." Journal of Physical Chemistry B 110(47):23644-23654. Abstract Recent advances in the use of molecular simulations and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to understand solvated ions in aqueous solutions are described. We report and discuss the results of the EXAFS spectra, Debye-Waller factors and the related properties governing solvation processes of different ions in water, as well as in different solvents (methanol). Molecular dynamics (MD) trajectories are coupled to electron scattering simulations to generate the EXAFS spectra, which are found to be in very good agreement with the corresponding experimental measurements. From these spectra, both the ion-oxygen and the ion-hydrogen distances for the first hydration shell are predicted to be within 0.1-0.2 Å. The ionic species studied range from monovalent to divalent, positive and negative: K+, Ca2+ and Cl-. This work demonstrates that the combination of MD-EXAFS and the corresponding experiment measurement provides a powerful tool in the analysis of the solvation structure of aqueous ionic solutions. We also investigate the value of electronic structure analysis of small aqueous clusters as a benchmark to the empirical potentials. In a novel computational approach, we compute the Debye-Waller factors combining a harmonic analysis of data obtained from electronic structure calculations on finite ionwater clusters, and we present a direct comparison with results from a harmonic classical statistical mechanical analysis of an empirical potential. Work was supported by the Office of Science, Office of Basic Energy Sciences, Chemical Sciences Division of the U.S. Department of Energy (DOE). The Pacific Northwest National Laboratory is operated by Battelle for DOE.
2006. "Recent Advances in molecular simulations of ion solvation at liquid interfaces." Chemical Reviews 106(4):1305-1322. doi:10.1021/cr0403640 Abstract In this paper, I present a review of the application of molecular dynamics simulation methods, including which polarizable potential models were used to describe interactions among species, to a variety of chemical and physical processes in solutions and at interfaces. The main emphasis of the review is on recent advances in the understanding of ion solvation, molecular association, and molecular solvation at liquid interfaces. The molecules discussed range from monovalent ions to molecular ions such as hydronium and nitrate ions. The computed properties include potentials of mean force, surface potentials, surface tensions, and density profiles. Comparisons with other simulation studies and experimental results were made and discussed in the review.
2005. "Investigating Pressure Effects on Structural and Dynamical Properties of Liquid Methanol with Many-Body Interactions." Journal of Chemical Physics 123(18):Art No. 184503. doi:10.1063/1.2039079 Abstract Molecular Dynamics simulations utilizing a many-body potential was used to study the pressure dependence of structural and dynamical properties for liquid methanol. The liquid density as a function of pressure agreed quite well with experiment, and a combination of radial and angular distribution functions were used to analyze molecular structure. From these distribution functions, it was observed that hydrogen bond strength increased with increasing pressure. This observation coincided with an increase in the molecular dipole as a function of pressure, which would definitely have a significant effect on the observed increased hydrogen bond strength. Also, methanol molecules were shown to more strongly favor exactly two hydrogen bonds at higher pressures, while fewer methanols with either zero, one, or three hydrogen bonds were observed at higher pressures. Furthermore, a majority of the compression with increased pressure was found to occur in regions perpendicular to the methanol oxygen-hydrogen bond vector. The methanol translational diffusion decreased significantly with increased pressure, while the rotational diffusion decreased at a similar magnitude around the oxygen-hydrogen and oxygen-carbon bond vectors, despite having very different overall diffusion. Finally, the hydrogen bond lifetime increased significantly with pressure, owing to the increased hydrogen bond strength.
2005. "Diffusion at the liquid-vapor interface of an aqueous ionic solution utilizing a dual simulation technique." Journal of Physical Chemistry B 109(32):15574-15579. doi:10.1021/jp051226x Abstract The recently proposed dual simulation technique [J. Phys. Chem. B 2004, 108, 6595.] is used to determine the diffusion coefficients for a variety of regions of a 2.2 sodium chloride aqueous solution with a vapor-liquid interface. For the calculation of the diffusion coefficient perpendicular to the interface, a modest modification to the dual simulation method was applied, while values parallel to the interface were determined without any modification to the method. Tests were performed, verifying the quality of modified method, showing it to be a well-defined self-consistent technique for the determination of the diffusion coefficient perpendicular to the interface. The diffusion of all species was shown to be isotropic far away from the interface, as expected, but at different regions in the interface, the diffusion coefficients parallel and perpendicular to the interface were not the same. Specifically, for water the diffusion coefficient perpendicular to the interface was higher in the liquid edge of the interface, but at the low density region, an opposite trend could be observed. For sodium and chloride ions, the diffusion parallel to the interface was higher than the values perpendicular to the interface near their concentration peaks. The diffusion of all species was generally higher at the vapor-liquid interface than in the middle of the liquid.
2005. "Molecular dynamics simulations of atmospheric oxidants at the air--water interface:Solvation and Accommodation of OH and O3." Journal of Physical Chemistry B 109(33):15876-15892. Abstract A comparative study of OH, O3, and H2O equilibrium aqueous solvation and gas phase accommodation on liquid water at 300 K is performed using a combination of ab initio calculations and molecular dynamics simulations. Polarizable force fields are developed for the interaction potential of OH and O3 with water. The free energy profiles for transfer of OH and O3 from the gas phase to the bulk liquid exhibit a pronounced minimum at the surface, but no barrier to solvation in the bulk liquid. The calculated surface excess of each oxidant is comparable to calculated and experimental values for short chain, aliphatic alcohols. Driving forces for the surface activity are discussed in terms of the radial distribution functions and dipole orientation distributions for each molecule in the bulk liquid and at the surface. Simulations of OH, O3, and H2O impinging on liquid water with a thermal impact velocity are used to calculate thermal accommodation, S, and mass accommodation, α, coefficients. The values of S for OH, O3, and H2O are 0.95, 0.90, and 0.99, respectively. The approaching molecules are accelerated towards the liquid surface when they are approximately 5 Å above it. The molecules that reach thermal equilibrium with the surface do so within 2 ps of striking the surface, while those that do not, scatter into the gas phase with excess translational kinetic energy in the direction perpendicular to the surface. The time constants for absorption and desorption range from approximately 35 – 140 ps and the values of α for OH, O3, and H2O are 0.83, 0.047, and 0.99, respectively. The results are consistent with previous formulations of gas phase accommodation from simulations, in which the process occurs by rapid thermal and structural equilibration followed by diffusion on the free energy profile. The implications of these results to atmospheric chemistry are discussed.
2005. "A unified molecular picture of the surfaces of aqueous acid, base, and salt solutions." Journal of Physical Chemistry B 109(16):7617-7623. Abstract A unified view of the structure of the air/solution interface of simple aqueous electrolytes containing monovalent inorganic ions is developed using molecular dynamics simulations and vibrational sum frequency generation spectroscopy. In salt solutions and bases the positively charged ions, such as alkali cations, are repelled from the air/solution interface, while the anions, such as halides or hydroxide, exhibit a varying propensity for the surface, correlated primarily with the polarizability of the ion. As a result, there is a net depletion of ions from the interfacial layer as a whole, which is connected via the Gibbs adsorption equation to an increase in surface tension with respect to neat water. The behavior of acids, such as aqueous HCl or HBr, is different due to a significant propensity of hydronium cations for the air/solution interface. Therefore, both cations and anions exhibit enhanced concentrations at the surface and, consequently, these acids reduce the surface tension of water. The key to the qualitatively different surface behavior of aqueous salt solutions and bases on one side and acids on the other thus lies in the appreciable adsorption of hydronium cations at the air/solution interface with their “hydrophobic” oxygen side oriented towards the gas phase. The results of the molecular dynamics calculations are supported by surface selective non-linear vibrational spectroscopy, which reveals among other things that the hydronium cations are present at the air/solution interface. The propensity of inorganic ions for the air/solution interface has important implications for heterogeneous chemical processes, in particular for atmospheric chemistry.
2005. "Liquid-Vapor Interface of Methanol-Water Mixtures: A Molecular Dynamics Study." Journal of Physical Chemistry B 109(12):5759-5765. Abstract Molecular dynamics simulations were carried out to investigate the structural and thermodynamic properties and variations in the dipole moments of the liquid/vapor interfaces of methanol-water mixtures. Various methanol-water compositions were simulated at room temperature. We found that methanol tends to concentrate at the interface, and the computed surface tension shows a composition dependence that is consistent with experimental measurements. The methanol molecule shows preferred orientation near the interface with the methyl group pointing into the vapor phase. The methanol in the mixture is found to have larger dipole moments than that of pure liquid methanol. The strong local field induced by the surrounding water molecules is partly the reason for this difference. The dependence of hydrogen bonding patterns between methanol and water on the interface and the composition of the mixture is also discussed in the paper.
2004. "Hydroxyl radical at the air-water interface." Journal of the American Chemical Society 126(50):16308-16309. Abstract The free energy profile for transfer of OH across the air/water interface at 300 K was calculated using classical molecular dynamics computer simulation with polarizable potential. The experimental hydration free energy (∆Gs ) is satisfactorily reproduced by the present force field. The free energy profile exhibits a minimum at the air/water interface, with the free energy of adsobtion (∆Gs ) being about 1 kcal/mol larger than the hydration free energy. The propensity of the OH radical for the air/water interface was further explored in simulation, in which OH radicals were originally placed inside the bulk liquid region of an infinite water slab about 30 Å thick. During 1 ns propagation, the OH radicals were observed to diffuse through the interior of the water slab, however, they were predominantly located in either of the two interfacial regions. Collisions of OH radical with the water surface were also investigated in a series of scattering simulations. From 250 initial conditions of a gas phase OH radical approaching the surface of liquid water with a thermal impact velocity, the thermal and mass accommodation coefficients at 300 K were determined to be 0.95 and 0.90, respectively. The partitioning of OH radicals between the bulk water and the interface was observed. The enhancement in the surface concentration of OH relative to the concentration in the aqueous phase, resulting from the surface activity of the hydroxyl radical, suggests that important OH chemistry may be occurring in the interfacial water layer of the water droplets, aqueous aerosol particles, and thin water films adsorbed on solid surfaces. This has profound consequences for modelling heterogeneous atmospheric chemical processes.
2004. "Ions at the liquid/vapor interface of methanol." Journal of Physical Chemistry A 108(42):9014-17. Abstract We study the detailed solvation properties of salt sodium iodide at the liquid/vapor interface of methanol that include surface tensions and density profiles as well as transport mechanism of an iodide anion across the methanol interface using molecular dynamics techniques. Polarizable potential models were used to describe interactions among species. The results indicated that the iodide anions were found at the interface more often than sodium cations. The computed potential of mean force showed a relatively small minimum well depth (i.e., -0.60 kcal/mol) locates inside the Gibbs dividing surface. The iodide anion carried some methanol molecules as it crosses the dividing interface. From this study, we can conclude that the population of iodide anions at the liquid water interface is far greater than its population at the liquid methanol interface.
2004. " Molecular mechanism of water and ammonia uptake by the liquid/vapor interface of water ." Chemical Physics Letters 385(3-4):309-313. Abstract Constrained molecular dynamics techniques were used to investigate the mechanism of the transfer of water and ammonia molecules from the gas phase to the liquid phase of water. The computed potentials of mean force or transfer free energies were nearly constant when the solute was more than several angstrom from the Gibbs dividing surface and decreased with no substantial minimum free energy as the solute molecules crossed the interface from the vapor to liquid phase. The computed free energy of solvation for water, estimated from the potential of mean force, was in excellent agreement with the experimental measurement while the corresponding computed solvation free energy for the ammonia molecule somewhat over estimated the experimental value. Possible reasons for the discrepancy are discussed.
2003. "Solvation of the hydronium ion at the water liquid/vapor interface ." Journal of Chemical Physics 119(12):6351-6353. Abstract In this study, we used constrained molecular dynamics techniques to investigate the transport of a hydronium ion across the water liquid/vapor interface. The computed transfer free energy was nearly unchanged as the hydronium ion approached the Gibbs dividing surface. The ion crossed the interface with no substantial minimum free energy, and transport of the hydronium ion involved a change in the solvent composition of the solvation shells around the ion.
2003. "Many-body interactions in liquid methanol and its liquid/vapor interface: A molecular dynamics study." Journal of Chemical Physics 119(18):9851-9857. Abstract Many-body interactions in liquid methanol and its liquid/vapor interface are evaluated using classical molecular dynamics techniques. The methanol molecule carries a molecular polarizability to account for induction energies and forces. The computed dipole moment for the methanol molecule changed from 1.7 D to 2.8 D, respectively from the vapor to the liquid phases. This result indicated that, there is significant many-body interactions in this complex molecular system. The computed average molecular dipole moment in liquid methanol at room temperature is in good agreement with experimental measurements. The computed average dipole moments of methanol molecules near the interface are close to their gas phase values, while methanol molecules far from the interface have dipole moments corresponding to their bulk values. The structural and thermodynamic properties of the liquid methanol as well as the surface tension of its liquid/vapor interface are in good agreement with the experiments, demonstrated high quality of our potential model and approaches.
2003. "EXAFS spectra of the dilute solutions of Ca2+ and Sr2+ in water and methanol ." Journal of Physical Chemistry B 107(50):14119-14123. Abstract A set of polarizable ion-water intermolecular interactions were developed that accurately described solvation enthalpies and structural properties of the dilute Ca2+ and Sr2+ in aqueous solution. The molecular dynamics (MD), coupled to electron scattering simulations of the Ca2+ and Sr2+ X-ray absorption fine structure spectroscopy (EXAFS) spectra are in good agreement with the corresponding experimental measurements. This work demonstrated that the combination of MD-EXAFS and the corresponding experiment measurement provides a power tool in the analysis of the solvation structure of the aqueous ionic solutions. The Ca2+-methanol interaction was also developed and the dilute Ca2+ MD-EXAFS spectrum in liquid methanol was also predicted using same approaches.
2003. "On rotational dynamics of an NH4+ ion in water." Journal of Chemical Physics 118(19):8813-8820. Abstract We used molecular dynamics simulations to characterize the rotational dynamics of the NH4+ ion in liquid water. The polarizable potential models were to describe the ion-water and water-water interactions. This study complements the work of Karim and Haymet (J. Chem. Phys., 93, 5961, 1990), who employed effective pir potential models. The computed rotational diffusion coefficients of the NH4+ ion in water, which were determined from the angular momentum autocorrelation function and the angular mean-square displacement, are 0.093 x 1012 rad2/s and 0.067 x 1012 rad2/s, repectively. These results are in good agreement with the 0.075 x 1012 rad2/s value determined from the nuclear magnetic resonance (NMR) spectroscopy studies of Perrin and Gipe (J. Am. Chem. Soc., 108, 1088, 1986; Science, 238, 1393, 1987).
2002. "Gibbs ensemble Monte Carlo simulations of coexistence properties of a polarizable potential model of water." Journal of Chemical Physics 117(7):3522-3523. Abstract The liquid/vapor coexistence density, the partial vapor pressure, and the heat of vaporization were calculated using Gibbs ensemble Monte Carlo simulation techniques. Long-range interactions such as charge-charge, charge-dipole, and dipole-dipole were evaluated using Ewald summation techniques. A polarizable potential model was used to describe the water-water interactions (Dang and Chang, J. Chem. Phys. 106, 8149, 1997). The model yields good agreement with the corresponding experimental data in the lower temperature region and moderate agreement in the higher temperature region. The critical temperature and density were estimated to be 565 K and 0.28 g/cm3.
2002. "Computational Study of ions binding to the liquid interface of water." Journal of Physical Chemistry B 106(40):10388-10394. Abstract We have performed extensive classical molecular dynamics simulations to examine the molecular transport mechanisms of the I-, Br-, Cl- and Na+ ions across the liquid/vapor interface of water. The potentials of mean force were calculated using the constrained mean force approach and polarizable potential models were used to describe the interactions among the species. The simulated potentials of mean force were found to be different, depending on the type of anion. The larger I- and Br- anions bind more strongly to the liquid/vapor interface of water than did the smaller Cl-ion. It is important to note here that most of the gas phase and solution phase properties of the Br- anion are quite similar to that of the Cl- ion. At the interface, however, the interactions of the Br- and Cl- anions with the water interface appeared to be significantly different. We found that the anions approach the interface more closely do than cations. We have also studied the transport mechanism of an I- across the water/dichloromethane interface. The computed potential of mean force showed no well-defined minimum as in the liquid/vapor case, but a stabilization free energy of about ?1 kcal/mol near the interface with respect to the bulk liquid was observed. The I- anion carried a water molecule with it as it crossed the interface. This result is in agreement with a recent experimental study on a similar system. Our work differs from earlier contributions in that our potential models have taken many-body effects into account, and in some cases, these effects cannot be neglected. To the best of our knowledge, this work significantly advances our understanding of molecular processes at the liquid interfaces.
2001. "Computer Simulation Studies Aqueous Solutions at Ambient and Supercritical Conditions Using Effective Pair Potential and Polarizable Potential Models for Water." Journal of Chemical Physics 114(17):7544-7555. Abstract N/A
2001. "Molecular mechanism of ion binding to the liquid/vapor interface of water." Journal of Physical Chemistry B 106(2):235-238. Abstract There is no abstract currently available for this item
2001. "A Mechanism for Ion Transport Across the Water/Dichloromethane Interface: A Molecular Dynamics Study Using Polarizable Potential Models." Journal of Physical Chemistry B 105(4):804-809. Abstract In this work, we used molecular dynamics techniques and mean force approaches to compute the ion transfer free energy for the water/dichloromethane liquid-liquid interface. We used polarizable potential models to describe the interactions among the species, and both forward and reverse directions were carried out to estimate the error bar of the computed free energy results. Based on the results of our calculations, we have proposed a mechanism that describes the transport of a chlorine ion across the interface. The computed ion transfer free energy is 14 ± 2 kcal/mol, which is in reasonable agreement with the experimentally reported value of 10 kcal/mol. A smooth transition from the aqueous phase to the non-aqueous phase on the free energy profile clearly indicates that the ion transfer mechanism is a nonactivated process. The computed hydration number for the chlorine ion indicates that some water molecules are associated with the ion inside the non-aqueous phase. This result is in excellent agreement with the experimental interpretation of the ion transfer mechanism reported recently by Osakai et al. (J. Phys. Chem. 1997, 101, 8341)
2000. "Molecular Dynamics Study of Water-Benzene Interactions at the Liquid/Vapor Interface of Water." Journal of Physical Chemistry B 104(18):4403-4407. Abstract N/A
2000. "Molecular Dynamics Study of Benzene-Benzene and Benzene- Potassium Ion Interactions Using Polarizable Potential Models." Journal of Chemical Physics 113(1):266-273. Abstract We construct a polarizable potential model for benzene using molecular dynamics techniques. The atomic site polarizabilities for carbon and hydrogen were taken from the recent work of Applequist J. (J. Phys. Chem. 1993, 97, 6016) which reproduced excellently the experimental molecular polarizability of benzene. Our model reproduces well the available experimental data such as the structure and thermodynamic properties of liquid benzene as well as the equilibrium properties of the liquid/vapor interface of benzene. The computed density profile shows that the interface is not sharp at a microscopic level and has a thickness about 5 ? at 300 K. The calculated surface tension is 25 ? 2 dyne/cm, in excellent agreement with the experimental value of 28 dyne/cm. The results of our model also compared well with the corresponding results obtained using OPLS potential parameters developed by Jorgensen, and Severance D. L. (J. Am. Chem. Soc. 1990, 112, 4768.)
1999. "Intermolecular Interactions of liquid dichloromethane and Equilibrium Properties of Liquid-Vapor and Liquid-Liquid Interfaces: A Molecular Dynamics Study." Journal of Chemical Physics 110(20):10113-10122.
1999. "Computer Simulation Studies of Ion Transport Across a Liquid/Liquid Interface." Journal of Chemical Physics 103(39):8195-8200.
1999. "Characterization of Water Octamer, Nanomer, Decamer and Iodine-water Interactions using Molecular Dynamics Techiniques." Journal of Chemical Physics 110(3):1526-1532. Abstract There is no abstract currently available for this item
1999. "Detailed Study of Potassium Solvation Using Molecular Dynamics Techniques." Journal of Physical Chemistry B 103(22):4714-4720.
1998. "Comparison of Classical and Quantum Statistical Mechanical Simulations of Aqueous Ionic Clusters." In Advances in Classical Trajectory Methods, Volume 3: Comparisons of classical and quantum dynamics , ed. William L. Hase, pp. 1-33. JAI Press, Inc., Stamford, CT. Abstract There is no abstract currently available for this item
1998. ""Mass Transfer Across the CCl4-H2O Liquid/Liquid Interface with Polarizable Potential Models"." In Recent Research Developments in Physical Chemistry, vol. 2, ed. S G Pandalai, pp. 867-888. Transworld Research Network, Trivandrum, India. Abstract There is no abstract currently available for this item