Ariel A. Chialvo

Oak Ridge National Laboratory, Oak Ridge, Florida, United States

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Publications (137)294.29 Total impact

  • Lukas Vlcek, Ariel A. Chialvo
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    ABSTRACT: The importance of single-ion hydration thermodynamic properties for understanding the driving forces of aqueous electrolyte processes, along with the impossibility of their direct experimental measurement, have prompted a large number of experimental, theoretical, and computational studies aimed at separating the cation and anion contributions. Here we provide an overview of historical approaches based on extrathermodynamic assumptions and more recent computational studies of single-ion hydration in order to evaluate the approximations involved in these methods, quantify their accuracy, reliability, and limitations in the light of the latest developments. We also offer new insights into the factors that influence the accuracy of ion-water interaction models and our views on possible ways to fill this substantial knowledge gap in aqueous physical chemistry.
    Fluid Phase Equilibria 06/2015; DOI:10.1016/j.fluid.2015.05.048 · 2.24 Impact Factor
  • Ariel A. Chialvo, Lukas Vlcek
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    ABSTRACT: We study the microstructural analysis of aqueous electrolytes and present a detailed account of the fundamentals underlying the neutron scattering with isotopic substitution (NDIS) approach for the experimental determination of ion coordination numbers in systems involving both halide anions and oxyanions. We place particular emphasis on the frequently overlooked ion-pairing phenomenon, identify its microstructural signature in the neutron-weighted distribution functions, and suggest novel techniques to deal with either the estimation of the ion-pairing magnitude or the correction of its effects on the experimentally measured coordination numbers. We illustrate the underlying ideas by applying these new developments to the interpretation of four NDIS test-cases via molecular simulation, as convenient dry runs for the actual scattering experiments, for representative aqueous electrolyte solutions at ambient conditions involving metal halides and nitrates.
    Fluid Phase Equilibria 05/2015; DOI:10.1016/j.fluid.2015.05.014 · 2.24 Impact Factor
  • Ariel A Chialvo, Filip Moucka, Lukas Vlcek, Ivo Nezbeda
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    ABSTRACT: We developed the Gaussian charge-on-spring (GCOS) version of the original self-consistent field implementation of the Gaussian Charge Polarizable water model and test its accuracy to represent the polarization behavior of the original model involving smeared charges and induced dipole moments. For that purpose we adapted the recently proposed multiple-particle-move (MPM) within the Gibbs and isochoric-isothermal ensembles Monte Carlo methods for the efficient simulation of polarizable fluids. We assessed the accuracy of the GCOS representation by a direct comparison of the resulting vapor-liquid phase envelope, microstructure, and relevant microscopic descriptors of water polarization along the orthobaric curve against the corresponding quantities from the actual GCP water model.
    The Journal of Physical Chemistry B 03/2015; 119(15). DOI:10.1021/acs.jpcb.5b00595 · 3.38 Impact Factor
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    ABSTRACT: We evaluate the ability of selected classical molecular models to describe the thermodynamic and structural aspects of gas-phase hydration of alkali halide ions and the formation of small water clusters. To understand the effect of many-body interactions (polarization) and charge penetration effects on the accuracy of a force field, we perform Monte Carlo simulations with three rigid water models using different functional forms to account for these effects: (i) point charge non-polarizable SPC/E, (ii) Drude point charge polarizable SWM4-DP, and (iii) Drude Gaussian charge polarizable BK3. Model predictions are compared with experimental Gibbs free energies and enthalpies of ion hydration, and with microscopic structural properties obtained from quantum DFT calculations. We find that all three models provide comparable predictions for pure water clusters and cation hydration, but differ significantly in their description of anion hydration. None of the investigated classical force fields can consistently and quantitatively reproduce the experimental gas phase hydration thermodynamics. The outcome of this study highlights the relation between the functional form that describes the effective intermolecular interactions and the accuracy of the resulting ion hydration properties.
    The Journal of Physical Chemistry A 12/2014; DOI:10.1021/jp509401d · 2.78 Impact Factor
  • Ariel A Chialvo, Lukas Vlcek
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    ABSTRACT: We explore the deconvolution of the water-nitrate correlations by the first-order difference approach involving neutron diffraction of heavy- and null-aqueous solutions of KNO3 under 14N/15N and natO/18O substitutions to achieve a full characterization of the first water coordination around the nitrate ion. For that purpose we performed isobaric-isothermal simulations of 3.5m KNO3 aqueous solutions at ambient conditions to generate the relevant radial distribution functions (RDF) required in the analysis (a) to identify the individual partial contributions to the total neutron weighted distribution function, (b) to isolate and assess the contribution of NO3-..K+ pair formation, (c) to test the accuracy of the NDIS-based coordination calculations and XRD-based assumptions, and (d) to describe the water coordination around both the nitrogen and oxygen sites of the nitrate ion.
    The Journal of Physical Chemistry B 12/2014; 119(2). DOI:10.1021/jp510355u · 3.38 Impact Factor
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    ABSTRACT: When water molecules are confined to nanoscale spacings, such as in the nanometer size pores of activated carbon fiber (ACF), their freezing point gets suppressed down to very low temperatures ($\sim$ 150 K), leading to a metastable liquid state with remarkable physical properties. We have investigated the ambient pressure diffusive dynamics of water in microporous Kynol\texttrademark ACF-10 (average pore size $\sim$11.6 {\AA}, with primarily slit-like pores) from temperature $T=$ 280 K in its stable liquid state down to $T=$ 230 K into the metastable supercooled phase. The observed characteristic relaxation times and diffusion coefficients are found to be respectively higher and lower than those in bulk water, indicating a slowing down of the water mobility with decreasing temperature. The observed temperature-dependent average relaxation time $<\tau>$ when compared to previous findings indicate that it is the size of the confining pores - not their shape - that primarily affects the dynamics of water for pore sizes larger than 10 {\AA}. The experimental observations are compared to complementary molecular dynamics simulations of a model system, in which we studied the diffusion of water within the 11.6 {\AA} gap of two parallel graphene sheets. We find generally a reasonable agreement between the observed and calculated relaxation times at the low momentum transfer $Q$ ($Q\le 0.9$ \AA${^{-1}}$). At high $Q$ however, where localized dynamics becomes relevant, this ideal system does not satisfactorily reproduce the measurements. The best agreement is obtained for the diffusion parameter $D$ associated with the hydrogen-site when a representative stretched exponential function, rather than the standard bi-modal exponential model, is used to parameterize the self-correlation function $I(Q,t)$.
    Physical Review E 12/2014; 91(2-1). DOI:10.1103/PhysRevE.91.022124 · 2.33 Impact Factor
  • Ariel A Chialvo, Lukas Vlcek
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    ABSTRACT: We present a detailed derivation of the complete set of expressions required for the implementation of an Ewald summation approach to handle the long-range electrostatic interactions of polar and ionic model systems involving Gaussian charges and induced dipole moments with a particular application to the isobaric-isothermal molecular dynamics (NPT-MD) simulation of our Gaussian Charge Polarizable (GCP) water model and its extension to aqueous electrolytes solutions. The set comprises the individual components of the potential energy, electrostatic potential, electrostatic field and gradient, the electrostatic force and the corresponding virial. Moreover, we show how the derived expressions converge to known point-based electrostatic counterparts when the parameters, defining the Gaussian charge and induced-dipole distributions, are extrapolated to their limiting point values. Finally, we test the simulation outcomes from the Ewald implementation against the corresponding reaction-field (RF) approach at three contrasting hydrogen-bonded water environments, including thermodynamic quantities, polarization behavior and microstructural properties, where the simulated microstructures are compared with the available neutron scattering and x-ray diffraction data.
    The Journal of Physical Chemistry B 11/2014; DOI:10.1021/jp509074p · 3.38 Impact Factor
  • Ariel A. Chialvo, Lukas Vlcek, Peter T. Cummings
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    ABSTRACT: We studied via molecular dynamics the link between the strain-driven hydration free-energy changes in the association process involving finite-size graphene surfaces, the resulting water graphene interfacial tension, and the combined effect of the surface strain and confinement on the thermodynamic response functions and the dynamics of confined water. We found that an in-plane biaxial tensile strain epsilon = 10% enhances significantly not only the water graphene hydrophobicity with respect to that of the unstrained counterpart but also the confinement effect on the thermodynamic response functions and slowing down of the dynamics of water over those of the corresponding bulk counterpart. The interfacial behavior of water in contact with strained-graphene plates resembles that observed for "pp" corrugated-plate configuration, as reported earlier [Chialvo et al. J. Phys. Chem. C 2013, 117, 23875], exibiting a significant enhancement of the fluid surface hydrophobicity and response functions relative to those of the unstrained surface. In contrast, the slowing down of the dynamics of the confined water does not show any differentiation with respect to the type of surface.
    The Journal of Physical Chemistry C 08/2014; 118(34):19701-19711. DOI:10.1021/jp501776m · 4.84 Impact Factor
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    ABSTRACT: Adsorption of supercritical CO 2 in nanoporous silica aerogel was investigated by a combination of experiments and molecular-level computer modeling. High-pressure gravimetric and vibrating tube densimetry techniques were used to measure the mean pore fluid density and excess sorption at 35 and 50 °C and pressures of 0−200 bar. Densification of the pore fluid was observed at bulk fluid densities below 0.7 g/cm 3 . Far above the bulk critical density, near-zero sorption or weak depletion effects were measured, while broad excess sorption maxima form in the vicinity of the bulk critical density. The CO 2 sorption properties are very similar for two aerogels with bulk densities of 0.1 and 0.2 g/cm 3 , respectively. The spatial distribution of the confined supercritical fluid was analyzed in terms of two nanodispersed phases with sorption-and bulk-phase densities and their volumes by means of the adsorbed phase model (APM), which used data from gravimetric sorption and small-angle neutron scattering experiments. To gain more detailed insight into supercritical fluid sorption, large-scale lattice gas GCMC simulations were utilized and tuned to resemble the experimental excess sorption data. The computed three-dimensional pore fluid density distributions show that the observed maximum of the excess sorption near the critical density originates from large density fluctuations pinned to the pore walls. At this maximum, the size of these fluctuations is comparable to the prevailing pore sizes.
    The Journal of Physical Chemistry C 06/2014; 118:15525. DOI:10.1021/jp503739x · 4.84 Impact Factor
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    Ariel A. Chialvo, Lukas Vlcek, Peter T. Cummings
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    ABSTRACT: We studied the link between the water-mediated (tensile or compressive) strain-driven hydration free energy changes in the association process involving finite-size graphene surfaces, the resulting water-graphene interfacial behaviour, and the combined effect of surface strain and fluid confinement on the thermodynamic response functions and the dynamics of water. We found that either small surface corrugation (compressive strain) or surface stretching (tensile strain) is able to enhance significantly the water-graphene hydrophobicity relative to that of the unstrained surface, an effect that exacerbates the confinement impact on the isothermal compressibility and isobaric thermal expansivity of confined water, as well as on the slowdown of its dynamics that gives rise to anomalous diffusivity.
    Molecular Physics 04/2014; 113(9-10):1033-1042. DOI:10.1080/00268976.2014.968228 · 1.64 Impact Factor
  • Ariel A. Chialvo, Lukas Vlcek, Peter T. Cummings
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    ABSTRACT: We carried out a systematic molecular simulation study of the behavior of a pair of finite-size graphene plates immersed in water at isobaric-isothermal conditions to provide insights into the nature of the water-graphene (corrugated) surface interactions. The goal was to address the link between the corrugation-driven hydration free energy changes in the association process involving graphene plates and the resulting water-graphene interfacial tension, to interrogate the effect of the surface corrugation and confinement on the thermodynamic response functions and the dynamics of confined water and to put the observed behavior in the context of Wenzel's modification of Young's equation. We found that graphene confinement induces a significant increase in the isothermal compressibility and isobaric thermal expansivity as well as a pronounced slowdown of the dynamics of water over that of the corresponding bulk counterpart, whose magnitudes depend on the type of surface corrugation involved. Our simulation results for different types of corrugated graphene plates involving identical surface areas do not support the meaning of the "r"-factor underlying Wenzel's equation for corrugated nanoscale surfaces.
    The Journal of Physical Chemistry C 11/2013; 117(45-45):23875-23886. DOI:10.1021/jp408893b · 4.84 Impact Factor
  • Ariel A. Chialvo, Lukas Vlcek, David R. Cole
    Reviews in Mineralogy and Geochemistry 11/2013; 77(1):361-398. DOI:10.2138/rmg.2013.77.10 · 3.57 Impact Factor
  • as Vlcek, Ariel A. Chialvo
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    ABSTRACT: Simple non-polarizable models of aqueous electrolytes underlie the majority of current geochemical and biochemical molecular simulations. To evaluate the reliability and predictive qualities of such studies, it is necessary to understand the limitations of the molecular force fields. Here we present the results of our effort to identify and overcome some of the main limiting factors of the existing simple models. First, we analyze relationships between experimental structural, dynamic, and thermodynamic properties and individual force field parameters. Our main focus is on the proper choice of reference experimental data for absolute single ion thermodynamics and utilizing known correlations between solvation entropies and tracer diffusivities. Subsequently, we use this information to construct empirical simple (Lennard-Jones potential and point charges) models of common mono- and divalent ions. These include alkali metal and alkaline earth cations paired with halide and oxo-anions. Finally, the limits of the resulting force field are evaluated and compared to other models. Acknowledgements. This work was supported by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy.
    13 AIChE Annual Meeting; 11/2013
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    Lukas Vlcek, Ariel A Chialvo, John M Simonson
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    ABSTRACT: Since the single-ion thermodynamic properties of bulk solutions are not directly accessible from experiments, extrapolations have been devised to estimate them from experimental measurements on small-clusters. Extrapolations based on the cluster-pair-based approximation (CPA) technique (Tissandier et al, J. Phys. Chem A 1998, 102, 7787-7794) and its variants are currently considered as one of the most reliable source of single-ion hydration thermodynamic data, and have been used as a benchmark for the development of molecular and continuum solvation models. Despite its importance, the CPA has not been thoroughly tested, while recent studies have indicated inconsistencies with molecular simulations. The present work challenges the key CPA assumptions that the hydration properties of single cations and anions in growing clusters rapidly converge to each other following a monotonous trend. Using a combination of simulation techniques to study the transition between alkali halide ions in small clusters and bulk solution, we show that this convergence is rather slow and involves a surprising change in trends, which can result in significant errors from the original estimated single-ion properties. When these cluster-size-dependent effects are taken into account, the inconsistencies between molecular models and experimental predictions disappear, and the value of the proton hydration enthalpy based on the CPA aligns with estimates based on other principles.
    The Journal of Physical Chemistry A 10/2013; 117(44). DOI:10.1021/jp408632e · 2.78 Impact Factor
  • as Vlcek, Ariel A. Chialvo
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    ABSTRACT: A balance between ion-ion and ion-water interactions plays a crucial role in the crystallization and dissolution of salts. Correct description of these interactions is therefore paramount for the understanding of natural processes leading to the precipitation of minerals, as well as for the design of new technologies, such as nuclear waste separation and storage. Our motivation is to investigate salt crystallization from mixed aqueous electrolyte solutions for the rational design of complexation agents used in selective crystallization of homologous series of oxoanions. A reliable description of molecular and ionic interactions is needed to understand atomic-scale mechanisms underlying the thermodynamics and dynamics of electrolyte solutions. Thus, our goal is to develop a consistent force field parameterization for the study of oxoanions of general formula XO42- (X=S, Se, Cr, Mo, W). While several force fields already exist for the description of simple alkali metal and alkali-halide series [1], and models for individual oxoanions have been also published [2], a consistent force field for oxoions suitable for comparative studies is not yet available. The choice of an appropriate potential model form depends on the intended applications, and must balance accuracy and computational efficiency. Since salt nucleation and crystallization occur over large time and length scales, the simplicity of the model is of high importance. While most of the above ions are highly polarizable, their mineral environment is consistently polar, justifying the use of effective pair potentials to account for those polarizable contributions. Therefore we consider pair potentials represented by a combination of point charges and Lennard-Jones interactions that are compatible with the SPC/E water model [3]. We also test the limit of the effective description of the interactions and discuss ways to incorporate polarizability. The resulting force field is optimized against experimental data including hydration free energy at infinite dilution [4], chemical potential at finite concentration based on the Kirkwood-Buff formalism [5], lattice constants and energies for selected crystals, and diffusion coefficient [4]. The potential parameters (at least 5 for each oxoion) were determined using global optimization based on the coupling parameter technique [6]. [1] Joung et al (2008) J. Phys. Chem. B 112(30), 9020-9041. [2] Cannon et al. (1994) J. Phys. Chem. 98(24), 6225-6230. [3] Berendsen et al. (1987) J. Phys. Chem. 91(24), 6269-6271. [4] Marcus, Y., Ion properties 1997, New York: Marcel Dekker. [5] Gee et al. (2011) J. Chem. Theory Comput. 7(5), 1369-1380. [6] Vlcek et al. (2011) J. Phys. Chem. B 115(27), 8775-8784. Acknowledgements. This work was supported as part of the “Center for Nanoscale Control of Geologic CO2”, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy.
    12 AIChE Annual Meeting; 10/2012
  • Ariel A. Chialvo, Lukas Vlcek, David R. Cole
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    ABSTRACT: We present a detailed molecular-based characterization via isobaric isothermal-molecular dynamics simulation of the microstructure and dynamics of water-rich aqueous CO2 solutions at silica surfaces and under extreme confinement between finite silica plates at state conditions relevant to geologic capture and sequestration of carbon dioxide. The study comprises three types of slit-pore plates to represent two extreme cases of surface polarity and a mismatched pair of plates to interrogate the fluid behavior at and confined between heterogeneous surfaces. We found layer formation of H2O and CO2 whose strength depends on the nature of the plate surface, i.e., stronger H2O layering at hydrophilic than at hydrophobic plates with simultaneous weaker water-mediated CO2/hydrophilic-surface interactions. We observed the opposite behavior with the hydrophobic plates in which the weaker water layering results from the CO2-mediated H2O/hydrophobic-surface interactions. Moreover, we illustrate how the interplay between these types of interactions and extreme fluid confinement, i.e., strong overlapping of interfacial structures, can induce a drying out of the pore environment whose immediate consequence is a significant CO, concentration enhancement relative to that of the bulk environment. Finally, we assessed the effect of the nature of the plate surfaces on the translational diffusion coefficient of water. We found that this property changes monotonically at purely interfacial regions but nonmonotonically under confinement.
    The Journal of Physical Chemistry C 07/2012; 116(26-26):13904-13916. DOI:10.1021/jp3001948 · 4.84 Impact Factor
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    A. A. Chialvo, J. M. Simonson
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    ABSTRACT: In this communication we illustrate the occurrence of a recently reported new phenomenon of surface-charge amplification, SCA, (originally dubbed overcharging, OC), [Jimenez-Angeles F. and Lozada-Cassou M., J. Phys. Chem. B, 2004, 108, 7286] by means of molecular dynamics simulation of aqueous electrolytes solutions involving multivalent cations in contact with charged graphene walls and the presence of short-chain lithium polystyrene sulfonates where the solvent water is described explicitly with a realistic molecular model. We show that the occurrence of SCA in these systems, in contrast to that observed in primitive models, involves neither contact co-adsorption of the negatively charged macroions nor divalent cations with a large size and charge asymmetry as required in the case of implicit solvents. In fact the SCA phenomenon hinges around the preferential adsorption of water (over the hydrated ions) with an average dipolar orientation such that the charges of the water's hydrogen and oxygen sites induce magnification rather than screening of the positive-charged graphene surface, within a limited range of surface-charge density.
    Condensed Matter Physics 02/2012; 14(3). DOI:10.5488/CMP.14.33002 · 0.77 Impact Factor
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    ABSTRACT: The interactions of electrolyte fluids with carbon-based electrodes control many complex interfacial processes encountered in electrochemical energy storage systems. However, our knowledge of the atomic/nanoscale reactivity at interfaces of electrolytes with electrodes remain scares due to the incomplete understanding of interfacial structures and processes in-situ and real-time encountered in real operation conditions. In this talk, we will present our efforts to obtain a molecular-scale perspective of the interactions of electrolytes with carbon surfaces near ``real world'' conditions. Structures of various electrolytes including slat aqueous and ionic liquids on atomically flat graphene (epitaxially grown on a SiC substrate), an ideal model fluid-solid interface system, were investigated by coupling high-resolution interface X-ray scattering techniques with molecular modeling-simulation approaches. These results provide a base-line for understanding relevant electrolyte/carbon interactions and will lead to fundamentally new insights and provide unique tests of atomistic fluid-solid interface models for energy storage systems.
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    ABSTRACT: The interaction of interfacial water with graphitic carbon at the atomic scale is studied as a function of the hydrophobicity of epitaxial graphene. High resolution x-ray reflectivity shows that the graphene-water contact angle is controlled by the average graphene thickness, due to the fraction of the film surface expressed as the epitaxial buffer layer whose contact angle (contact angle θc = 73°) is substantially smaller than that of multilayer graphene (θc = 93°). Classical and ab initio molecular dynamics simulations show that the reduced contact angle of the buffer layer is due to both its epitaxy with the SiC substrate and the presence of interfacial defects. This insight clarifies the relationship between interfacial water structure and hydrophobicity, in general, and suggests new routes to control interface properties of epitaxial graphene.
    Physical Review B 01/2012; 85(3). DOI:10.1103/PhysRevB.85.035406 · 3.66 Impact Factor
  • L. Vlcek, G. Rother, A. Chialvo, D. R. Cole
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    ABSTRACT: Injection of CO2 into geologic formations has been proposed as a key element to reduce the impact of greenhouse gases emissions. Quantitative understanding of CO2 adsorption in porous mineral environments at thermodynamic conditions relevant to proposed sequestration sites is thus a prerequisite for the assessment of their viability. In this study we use a combination of neutron scattering, adsorption experiments, and computer modeling to investigate the thermodynamics of near-critical carbon dioxide in the pores of SiO2 aerogel, which serves as a model of a high-porosity reservoir rock. Small angle neutron scattering (SANS) experiments provide input for the optimization of the computer model of the aerogel matrix, and also serve as a sensitive probe of local density changes of confined CO2 as a function of external pressure. Additional details of the aerogel basic building blocks and SiO2 surface are derived from TEM images. An independent source of global adsorption data is obtained from gravimetric experiments. The structural and thermodynamic aspects of CO2 sorption are linked using computer simulations, which include the application of the optimized diffusion limited cluster-cluster aggregation algorithm (DLCA), classical density functional theory (DFT) modeling of large-scale CO2 density profiles, and molecular dynamics simulations of the details of interactions between CO2 molecules and the amorphous silica surfaces. This integrated approach allows us to span scales ranging from 1Å to 1μm, as well as to infer the detailed structure of silica threads forming the framework of the silica matrix.

Publication Stats

3k Citations
294.29 Total Impact Points

Institutions

  • 1996–2014
    • Oak Ridge National Laboratory
      • Chemical Sciences Division
      Oak Ridge, Florida, United States
    • University of Tennessee
      • Department of Chemical and Biomolecular Engineering
      Knoxville, Tennessee, United States
  • 2007
    • Russian Academy of Sciences
      • Vernadsky Institute of Geochemistry and Analytical Chemistry
      Moskva, Moscow, Russia
    • University of Chicago
      • Department of Chemistry
      Chicago, Illinois, United States
  • 1994–2002
    • The University of Tennessee Medical Center at Knoxville
      Knoxville, Tennessee, United States
  • 1993–1994
    • University of Virginia
      • Department of Chemical Engineering
      Charlottesville, Virginia, United States
  • 1989–1992
    • Princeton University
      • Department of Chemical and Biological Engineering
      Princeton, New Jersey, United States