The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Liem X Dang - One of the best experts on this subject based on the ideXlab platform.
-
solvation of the hydronium ion at the water liquid vapor Interface
Journal of Chemical Physics, 2003Co-Authors: Liem X DangAbstract: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.
-
molecular dynamics study of water clusters liquid and liquid vapor Interface of water with many body potentials
Journal of Chemical Physics, 1997Co-Authors: Liem X Dang, Tsunmei ChangAbstract:The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structuralproperties of the liquid and the liquid/vapor Interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of vaporization, as well as the diffusion coefficient, are in excellent agreement with experimental values. Structuralproperties of liquidwater, such as the radial distribution functions, neutron, and x-ray scattering intensities, were calculated and critically evaluated against the experimental measurements. In all cases, we found the agreement between the observed data and the computed properties to be quite reasonable. The computed density profile of the water’s liquid/vapor Interface shows that the Interface is not sharp at a microscopic level and has a thickness of 3.2 A at 298 K. These results are consistent with those reported in earlier work on the same systems. The calculated surface tension at room temperature is in reasonable agreement with the corresponding experimental data. As expected, the computed average dipole moments of water molecules near the Interface are close to their gas phase values, while water molecules far from the Interface have dipole moments corresponding to their bulk values.
-
molecular dynamics study of water clusters liquid and liquid vapor Interface of water with many body potentials
Journal of Chemical Physics, 1997Co-Authors: Liem X Dang, Tsunmei ChangAbstract:The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structural properties of the liquid and the liquid/vapor Interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of v...
-
molecular dynamics simulations of the liquid vapor Interface of spc e water
The Journal of Physical Chemistry, 1996Co-Authors: Ramona S Taylor, Liem X Dang, Bruce C GarrettAbstract:Molecular dynamics computer simulations have been used to explore the structural and dynamical properties of water's liquid/vapor Interface using the simple extended point charge (SPC/E) model. Comparisons to the existing experimental and simulation data suggest that the SPC/E potential energy function provides a semiquantitative description of this Interface. The orientation of H2O molecules at the Interface is found to be bimodal in nature. The self-diffusion constant of water is calculated to be larger at the surface than in the bulk.
Tsunmei Chang - One of the best experts on this subject based on the ideXlab platform.
-
molecular dynamics study of water clusters liquid and liquid vapor Interface of water with many body potentials
Journal of Chemical Physics, 1997Co-Authors: Liem X Dang, Tsunmei ChangAbstract:The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structuralproperties of the liquid and the liquid/vapor Interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of vaporization, as well as the diffusion coefficient, are in excellent agreement with experimental values. Structuralproperties of liquidwater, such as the radial distribution functions, neutron, and x-ray scattering intensities, were calculated and critically evaluated against the experimental measurements. In all cases, we found the agreement between the observed data and the computed properties to be quite reasonable. The computed density profile of the water’s liquid/vapor Interface shows that the Interface is not sharp at a microscopic level and has a thickness of 3.2 A at 298 K. These results are consistent with those reported in earlier work on the same systems. The calculated surface tension at room temperature is in reasonable agreement with the corresponding experimental data. As expected, the computed average dipole moments of water molecules near the Interface are close to their gas phase values, while water molecules far from the Interface have dipole moments corresponding to their bulk values.
-
molecular dynamics study of water clusters liquid and liquid vapor Interface of water with many body potentials
Journal of Chemical Physics, 1997Co-Authors: Liem X Dang, Tsunmei ChangAbstract:The molecular dynamics computer simulation technique is used to develop a rigid, four-site polarizable model for water. The suggested model reasonably describes the important properties of water clusters, the thermodynamic and structural properties of the liquid and the liquid/vapor Interface of water. The minimum energy configurations and the binding energies for these clusters are in reasonable agreement with accurate electronic structure calculations. The model predicts that the water trimer, tetramer, and pentamer have cyclic planar minimum energy structures. A prismlike structure is predicted to be lowest in energy for the water hexamer, and a cagelike structure is the second lowest in energy, with an energy of about 0.2 kcal/mol higher than the prismlike structure. The results are consistent with recent quantum Monte Carlo simulations as well as electronic structure calculations. The computed thermodynamic properties for the model, at room temperature, including the liquid density, the enthalpy of v...
J L Skinner - One of the best experts on this subject based on the ideXlab platform.
-
vibrational sum frequency spectroscopy of the liquid vapor Interface for dilute hod in d2o
Journal of Chemical Physics, 2008Co-Authors: B M Auer, J L SkinnerAbstract:An electronic structure/molecular dynamics approach, originally developed to describe the vibrational spectroscopy of the OH stretch of dilute HOD in liquid D2O, is applied to the vibrational sum-frequency spectroscopy of the liquid/vapor Interface of this system. In both cases the OH stretch is effectively decoupled from the OD stretches, allowing it to act as a local probe of structure and dynamics. A mixed quantum/classical expression for the vibrational sum-frequency response that includes the effect of motional narrowing is used to calculate the resonant susceptibility. Despite being developed for the bulk liquid, our method works well for the surface in that the real and imaginary parts of the resonant susceptibility are in good agreement with experiment. We explore the nature of hydrogen bonding at the Interface as well as its impact on the sum-frequency spectrum. It is found that the spectrum is dominated by single-donor molecules with a total of two or three hydrogen bonds.
José Alejandre - One of the best experts on this subject based on the ideXlab platform.
-
constrained dipole moment density functional theory for charge distributions in force fields for the study of molecular fluids
Journal of Chemical Physics, 2020Co-Authors: Javier Carmonaespindola, Edgar Nunezrojas, Valeria Garciamelgarejo, Jose L Gazquez, José AlejandreAbstract:A new procedure, based on electronic structure calculations that only requires a dipole moment value for a given molecule as input and, from which the charges for all the atoms in it are uniquely determined, is developed and applied to the study of molecular fluids with classical dynamics. The dipole moment value considered for the isolated molecule is the one that reproduces the dielectric constant of its corresponding fluid. Following previous work, the Lennard-Jones parameters are determined to reproduce the liquid density and the surface tension at the Liquid-Vapor Interface. The force field thus obtained leads to a reasonable description of several properties such as heats of vaporization, self-diffusion coefficients, shear viscosities, isothermal compressibilities, and volumetric expansion coefficients of pure substances.
-
force field benchmark of the trappe_ua for polar liquids density heat of vaporization dielectric constant surface tension volumetric expansion coefficient and isothermal compressibility
Journal of Physical Chemistry B, 2018Co-Authors: Edgar Nunezrojas, Jorge Alberto Aguilarpineda, Edith Nadir De Jesus Gonzalez, José AlejandreAbstract:The transferable potential for a phase equilibria force field in its united-atom version, TraPPE_UA, is evaluated for 41 polar liquids that include alcohols, thiols, ethers, sulfides, aldehydes, ketones, and esters to determine its ability to reproduce experimental properties that were not included in the parametrization procedure. The intermolecular force field parameters for pure components were fit to reproduce experimental boiling temperature, vapor–liquid coexisting densities, and critical point (temperature, density, and pressure) using Monte Carlo simulations in different ensembles. The properties calculated in this work are liquid density, heat of vaporization, dielectric constant, surface tension, volumetric expansion coefficient, and isothermal compressibility. Molecular dynamics simulations were performed in the gas and liquid phases, and also at the liquid–vapor Interface. We found that relative error between calculated and experimental data is 1.2% for density, 6% for heat of vaporization, an...
-
Surface tension of the restrictive primitive model for ionic liquids.
Physical review letters, 2003Co-Authors: Minerva González-melchor, José Alejandre, Fernando BresmeAbstract:Hybrid molecular dynamics and Monte Carlo simulations are performed to study the Liquid-Vapor Interface of the restricted primitive model (RPM) of ionic fluids. We report for the first time simulation results of the surface tension associated to this Interface. The RPM accurately predicts experimental surface tensions of ionic salts and good agreement with theoretical predictions that include the idea of ion association is found. The simulation results indicate that the structure of an ionic Liquid-Vapor Interface is rather rough. This is reflected in the interfacial thickness, larger than that observed in simple fluids and water.
-
computer simulations of liquid vapor Interface in lennard jones fluids some questions and answers
Journal of Chemical Physics, 1999Co-Authors: Andrij Trokhymchuk, José AlejandreAbstract:Canonical molecular dynamics (MD) and Monte Carlo (MC) simulations for liquid/vapor equilibrium in truncated Lennard-Jones fluid have been carried out. Different results for coexistence properties (orthobaric densities, normal and tangential pressure profiles, and surface tension) have been reported in each method. These differences are attributed in literature to different set up conditions, e.g., size of simulation cell, number of particles, cut-off radius, time of simulations, etc., applied by different authors. In the present study we show that observed disagreement between simulation results is due to the fact that different authors inadvertently simulated different model fluids. The origin of the problem lies in details of truncation procedure used in simulation studies. Care has to be exercised in doing the comparison between both methods because in MC calculations one deals with the truncated potential, while in MD calculations one uses the truncated forces, i.e., derivative of the potential. The ...
Per M Claesson - One of the best experts on this subject based on the ideXlab platform.
-
hydration state of nonionic surfactant monolayers at the liquid vapor Interface structure determination by vibrational sum frequency spectroscopy
Journal of the American Chemical Society, 2005Co-Authors: Eric Tyrode, Magnus C Johnson, Atte Kumpulainen, Mark W Rutland, Per M ClaessonAbstract:The OH stretching region of water molecules in the vicinity of nonionic surfactant monolayers has been investigated using vibrational sum frequency spectroscopy (VSFS) under the polarization combinations ssp, ppp, and sps. The surface sensitivity of the VSFS technique has allowed targeting the few water molecules present at the surface with a net orientation and, in particular, the hydration shell around alcohol, sugar, and poly(ethylene oxide) headgroups. Dramatic differences in the hydration shell of the uncharged headgroups were observed, both in comparison to each another and in comparison to the pure water surface. The water molecules around the rigid glucoside and maltoside sugar rings were found to form strong hydrogen bonds, similar to those observed in tetrahedrally coordinated water in ice. In the case of the poly(ethylene oxide) surfactant monolayer a significant ordering of both strongly and weakly hydrogen bonded water was observed. Moreover, a band common to all the surfactants studied, clearly detected at relatively high frequencies in the polarization combinations ppp and sps, was assigned to water species located in proximity to the surfactant hydrocarbon tail phase, with both hydrogen atoms free from hydrogen bonds. An orientational analysis provided additional information on the water species responsible for this band.