13 research outputs found

    On Examining Solvation and Dielectric Constants of Polar and Ionic Liquids using the Stockmayer Fluid Model

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    We develop Stockmayer fluid (SF) models to predict and analyze dielectric properties of polar solvents, ionic liquids, and polyermized ionic liquids. A Stockmayer fluid treats molecules as simple Lennard-Jones spheres with dipole moments and point charges. With this model we calculate the solvation energies of 26 ions in 7 polar solvents and compare with experiment. There is qualitative agreement and we find that the SF model can account for the effects of dielectric saturation, which the commonly used Born solvation energy equation lacks. We also calculate the dielectric constants of these 7 solvents and find quantitative agreement with experiment. We also compare the SF model with experiment in regards to temperature dependence, electric field dependence, and salt concentration dependence of the dielectric constant of water. We also model the ionic liquid Ethylammonium Nitrate and calculate its dielectric constant, and compare with a polymerized version of the same material, simply chaining the cations and allowing their dipoles to rotate freely. We then implement a novel model for the polymerized ionic liquid Poly N-vinyl Ethylimidazolium Bromide, with restricted dipolar motion. We find that polymerized ionic liquids with restricted dipoles exhibit dielectric decrement compared with their monomeric ionic liquid counterparts, but with increased degrees of freedom can experience enhancment of their dielectric constant. We also detail some drawbacks of the model as well as posit potential future research avenues

    Solvation Energy of Ions in a Stockmayer Fluid

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    We calculate the solvation energy of monovalent and divalent ions in various liquids with coarse-grained molecular dynamics simulations. Our theory treats the solvent as a Stockmayer fluid, which accounts for the intrinsic dipole moment of molecules and the rotational dynamics of the dipoles. Despite the simplicity of the model, we obtain qualitative agreement between the simulations and experimental data for the free energy and enthalpy of ion solvation, which indicates that the primary contribution to the solvation energy arises mainly from the first and possibly second solvation shells near the ions. Our results suggest that a Stockmayer fluid can serve as a reference model that enables direct comparison between theory and experiment and may be invoked to scale up electrostatic interactions from the atomic to the molecular length scale

    Molecular dynamics simulations of the dielectric constants of salt-free and salt-doped polar solvents

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    We develop a Stockmayer fluid model that accounts for the dielectric responses of polar solvents (water, MeOH, EtOH, acetone, 1-propanol, DMSO, and DMF) and NaCl solutions. These solvent molecules are represented by Lennard-Jones (LJ) spheres with permanent dipole moments and the ions by charged LJ spheres. The simulated dielectric constants of these liquids are comparable to experimental values, including the substantial decrease in the dielectric constant of water upon the addition of NaCl. Moreover, the simulations predict an increase in the dielectric constant when considering the influence of ion translations in addition to the orientation of permanent dipoles

    Surrogate molecular dynamics simulation model for dielectric constants with ensemble neural networks

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    We develop ensemble neural networks (ENN) that serve as computationally fast surrogate models of Stockmayer fluid molecular dynamics (MD) simulations for determining the dielectric constants of polar solvents and NaCl solutions. The ENNs are trained using 50-times less data than is used to calculate the dielectric constants from MD simulations. The predictions of ENNs trained on this small amount of data and using batch normalization or bagging are in relatively good agreement with the full MD results. These ENN methods are thus able to extract reliable values from statistically noisy data

    The imitation game - a computational chemical approach to recognizing life

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    The definition of 'life' has invoked innumerable vigorous discussions, ranging from the religious to the scientific, philosophical and metaphysical, and still today no universally acceptable definition is available. This controversy is inescapable because of the absence of a theory of the nature of living systems. There is, however, an urgent practical need for a universally acceptable way of recognizing life or the potential for life. The absence of any agreed- upon guiding definitions of what it is to be alive, and more generally of what is life, makes it difficult for researchers in a variety of communities to objectively recognize success. For example, it remains far from trivial within the exobiology and astrobiology communities to objectively assess whether a new form of extraterrestrial life has been discovered; for researchers studying the origins of life, it is difficult to demonstrate whether life's beginnings have been successfully explained; and in the synthetic biology and artificial chemistry communities, demonstrating the creation of a wholly synthetic life form is a daunting process
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