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Marco A Saitta - One of the best experts on this subject based on the ideXlab platform.

  • ab initio Molecular Dynamics Study of an aqueous nacl solution under an electric field
    Physical Chemistry Chemical Physics, 2016
    Co-Authors: Giuseppe Cassone, Marco A Saitta, Franz Saija, P V Giaquinta, Fabrizio Creazzo
    Abstract:

    We report on an ab initio Molecular Dynamics Study of an aqueous NaCl solution under the effect of static electric fields. We found that at low-to-moderate field intensity regimes chlorine ions have a greater mobility than sodium ions which, being a sort of “structure makers”, are able to drag their own coordination shells. However, for field strengths exceeding 0.15 V A−1 the mobility of sodium ions overcomes that of chlorine ions as both types of ions do actually escape from their respective hydration cages. The presence of charged particles lowers the water dissociation threshold (i.e., the minimum field strength which induces a transfer of protons) from 0.35 V A−1 to 0.25 V A−1; moreover, a protonic current was also recorded at the estimated dissociation threshold of the solution. The behaviour of the current–voltage diagram of the protonic response to the external electric field is Ohmic as in pure water, with a resulting protonic conductivity of about 2.5 S cm−1. This value is approximately one third of that estimated in pure water (7.8 S cm−1), which shows that the partial breaking of hydrogen bonds induced by the solvated ions hinders the migration of protonic defects. Finally, the conductivity of Na+ and Cl− ions (0.2 S cm−1) is in fair agreement with the available experimental data for a solution molarity of 1.7 M.

  • ab initio Molecular Dynamics Study of dissociation of water under an electric field
    Physical Review Letters, 2012
    Co-Authors: Marco A Saitta, Franz Saija, P V Giaquinta
    Abstract:

    : The behavior of liquid water under an electric field is a crucial phenomenon in science and engineering. However, its detailed description at a microscopic level is difficult to achieve experimentally. Here we report on the first ab initio Molecular-Dynamics Study on water under an electric field. We observe that the hydrogen-bond length and the Molecular orientation are significantly modified at low-to-moderate field intensities. Fields beyond a threshold of about 0.35  V/A are able to dissociate molecules and sustain an ionic current via a series of correlated proton jumps. Upon applying even more intense fields (∼1.0  V/A), a 15%-20% fraction of molecules are instantaneously dissociated and the resulting ionic flow yields a conductance of about 7.8  Ω-1 cm-1, in good agreement with experimental values. This result paves the way to quantum-accurate microscopic studies of the effect of electric fields on aqueous solutions and, thus, to massive applications of ab initio Molecular Dynamics in neurobiology, electrochemistry, and hydrogen economy.

Edward J Maginn - One of the best experts on this subject based on the ideXlab platform.

  • density local composition and diffusivity of aqueous choline chloride solutions a Molecular Dynamics Study
    Fluid Phase Equilibria, 2004
    Co-Authors: Timothy I Morrow, Edward J Maginn
    Abstract:

    We report the results of a Molecular Dynamics Study of aqueous solutions of n-hydroxyethyl-trimethyl-ammonium chloride (choline chloride). An all-atom forcefield is developed for choline chloride, while the SPC/E model is used for water. The calculations predict densities that agree to within 1% of the values subsequently reported by the National Institute of Standards and Technology as part of the Industrial Fluid Properties Simulation Challenge. In addition to densities, other computed quantities include liquid structure and self-diffusivities.

  • Molecular Dynamics Study of the Ionic Liquid 1-n-Butyl-3-methylimidazolium Hexafluorophosphate
    The Journal of Physical Chemistry B, 2002
    Co-Authors: Timothy I Morrow, Edward J Maginn
    Abstract:

    We report the results of a Molecular Dynamics Study of the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], a widely studied ionic liquid. An all-atom force field is developed using a combination of density functional theory calculations and CHARMM 22 parameter values. Molecular Dynamics simulations are carried out in the isothermal−isobaric ensemble at three different temperatures. Quantities computed include infrared frequencies, molar volumes, volume expansivities, isothermal compressibililties, self-diffusivities, cation−anion exchange rates, rotational Dynamics, and radial distribution functions. Computed thermodynamic properties are in good agreement with available experimental values.

Daan Frenkel - One of the best experts on this subject based on the ideXlab platform.

  • homogeneous bubble nucleation driven by local hot spots a Molecular Dynamics Study
    arXiv: Chemical Physics, 2009
    Co-Authors: Zunjing Wang, Chantal Valeriani, Daan Frenkel
    Abstract:

    We report a Molecular Dynamics Study of homogenous bubble nucleation in a Lennard-Jones fluid. The rate of bubble nucleation is estimated using forward-flux sampling (FFS). We find that cavitation starts with compact bubbles rather than with ramified structures as had been suggested by Shen and Debenedetti (J. Chem. Phys. 111:3581, 1999). Our estimate of the bubble-nucleation rate is higher than predicted on the basis of Classical Nucleation Theory (CNT). Our simulations show that local temperature fluctuations correlate strongly with subsequent bubble formation - this mechanism is not taken into account in CNT.

  • homogeneous bubble nucleation driven by local hot spots a Molecular Dynamics Study
    Journal of Physical Chemistry B, 2009
    Co-Authors: Zunjing Wang, Chantal Valeriani, Daan Frenkel
    Abstract:

    We report a Molecular Dynamics Study of homogeneous bubble nucleation in a Lennard-Jones fluid. The rate of bubble nucleation is estimated using forward-flux sampling (FFS). We find that cavitation starts with compact bubbles rather than with ramified structures, as had been suggested by Shen and Debenedetti (J. Chem. Phys. 1999, 111, 3581). Our estimate of the bubble-nucleation rate is higher than predicted on the basis of classical nucleation theory (CNT). Our simulations show that local temperature fluctuations correlate strongly with subsequent bubble formation; this mechanism is not taken into account in CNT.

P V Giaquinta - One of the best experts on this subject based on the ideXlab platform.

  • ab initio Molecular Dynamics Study of an aqueous nacl solution under an electric field
    Physical Chemistry Chemical Physics, 2016
    Co-Authors: Giuseppe Cassone, Marco A Saitta, Franz Saija, P V Giaquinta, Fabrizio Creazzo
    Abstract:

    We report on an ab initio Molecular Dynamics Study of an aqueous NaCl solution under the effect of static electric fields. We found that at low-to-moderate field intensity regimes chlorine ions have a greater mobility than sodium ions which, being a sort of “structure makers”, are able to drag their own coordination shells. However, for field strengths exceeding 0.15 V A−1 the mobility of sodium ions overcomes that of chlorine ions as both types of ions do actually escape from their respective hydration cages. The presence of charged particles lowers the water dissociation threshold (i.e., the minimum field strength which induces a transfer of protons) from 0.35 V A−1 to 0.25 V A−1; moreover, a protonic current was also recorded at the estimated dissociation threshold of the solution. The behaviour of the current–voltage diagram of the protonic response to the external electric field is Ohmic as in pure water, with a resulting protonic conductivity of about 2.5 S cm−1. This value is approximately one third of that estimated in pure water (7.8 S cm−1), which shows that the partial breaking of hydrogen bonds induced by the solvated ions hinders the migration of protonic defects. Finally, the conductivity of Na+ and Cl− ions (0.2 S cm−1) is in fair agreement with the available experimental data for a solution molarity of 1.7 M.

  • ab initio Molecular Dynamics Study of dissociation of water under an electric field
    Physical Review Letters, 2012
    Co-Authors: Marco A Saitta, Franz Saija, P V Giaquinta
    Abstract:

    : The behavior of liquid water under an electric field is a crucial phenomenon in science and engineering. However, its detailed description at a microscopic level is difficult to achieve experimentally. Here we report on the first ab initio Molecular-Dynamics Study on water under an electric field. We observe that the hydrogen-bond length and the Molecular orientation are significantly modified at low-to-moderate field intensities. Fields beyond a threshold of about 0.35  V/A are able to dissociate molecules and sustain an ionic current via a series of correlated proton jumps. Upon applying even more intense fields (∼1.0  V/A), a 15%-20% fraction of molecules are instantaneously dissociated and the resulting ionic flow yields a conductance of about 7.8  Ω-1 cm-1, in good agreement with experimental values. This result paves the way to quantum-accurate microscopic studies of the effect of electric fields on aqueous solutions and, thus, to massive applications of ab initio Molecular Dynamics in neurobiology, electrochemistry, and hydrogen economy.

Hiroshi Noguchi - One of the best experts on this subject based on the ideXlab platform.

  • polymer effects on karman vortex Molecular Dynamics Study
    Journal of Chemical Physics, 2018
    Co-Authors: Yuta Asano, Hiroshi Watanabe, Hiroshi Noguchi
    Abstract:

    We investigated the Karman vortex behind a circular cylinder in a polymer solution by a Molecular Dynamics simulation. The vortex characteristics are distinctly different for short and long polymers. The solution with the long polymer exhibits a reduction in the vortex shedding frequency and broadening of the lift coefficient spectrum. On the other hand, the characteristics of the short-polymer solution are almost the same as those of the Newtonian fluid. These facts are consistent with the experiments. Because the distributions of the gyration radius and the orientational order of the long-polymer solution are highly inhomogeneous in the flow field, we conclude that the extensional property of the polymer plays an important role in changing the flow characteristics.

  • polymer effects on karman vortex Molecular Dynamics Study
    arXiv: Soft Condensed Matter, 2018
    Co-Authors: Yuta Asano, Hiroshi Watanabe, Hiroshi Noguchi
    Abstract:

    We investigated the Karman vortex behind a circular cylinder in a polymer solution by a Molecular Dynamics simulation. The vortex characteristics are distinctly different for short and long polymers. The solution with the long polymer exhibits a reduction in the vortex shedding frequency and broadening of the lift coefficient spectrum. On the other hand, the characteristics of the short-polymer solution are almost same as those of the Newtonian fluid. These facts are consistent with the experiments. Because the distributions of the gyration radius and the orientational order of the long-polymer solution are highly inhomogeneous in the flow field, we conclude that the extensional property of the polymer plays an important role in changing the flow characteristics.