Comment on "The gas-liquid surface tension of argon: A reconciliation between experiment and simulation" [J. Chem. Phys. 140, 244710 (2014)] (original) (raw)
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The gas-liquid surface tension of argon: A reconciliation between experiment and simulation
The Journal of Chemical Physics, 2014
We present a simulation of the liquid-vapor interface of argon with explicit inclusion of the threebody interactions. The three-body contributions to the surface tension are calculated using the Kirkwood-Buff approach. Monte Carlo calculations of the long-range corrections to the three-body contribution are calculated from the radial distribution function g (2) (z 1 , cos θ 12 , r 12). Whereas the effective two-body potentials overestimate the surface tension by more than 15%, the inclusion of the three-body potential provides an excellent agreement with the experimental results for temperatures up to 15 K below the critical temperature. We conclude that the three-body interactions must be explicitly included in accurately modelling the surface tension of argon.
Argon force field revisited: a molecular dynamic study
Journal of Physics Communications
We report the improvement of five argon force fields by scaling Lennard-Jones 6–12 potential (LJP) energy (ϵ) and distance (σ) parameters to reproduce liquid-vapor phase diagram and surface tension simultaneously, with molecular dynamics. Original force fields reproduce only liquid-vapor phase diagram among other properties except surface tension. Results showed that all new force fields obtained by scaling LJP parameters reproduce well the experimental surface tension and the liquid-vapor phase diagram, also the LJP energy and distance parameters converge in a nearby region in the ϵ-σ phase space, which is different from the original values. This study gives the intervals where the numerical values of ϵ and σ reproduce both properties mentioned above. Furthermore, a study to calculate surface tension to avoid finite size effects is shown.
Computer simulations of liquid/vapor interface in Lennard-Jones fluids: Some questions and answers
The Journal of Chemical Physics, 1999
Canonical molecular dynamics ͑MD͒ and Monte Carlo ͑MC͒ 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 tension͒ 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 truncated force does not uniquely define the primordial potential. It results in MD and MC simulations being performed for different potential models. No differences in the coexistence properties obtained from MD and MC simulations are found when the same potential model is used. An additional force due to the discontinuity of the truncated potential at cut-off distance becomes crucial for inhomogeneous fluids and has to be included into the virial calculations in MC and MD, and into the computation of trajectories in MD simulations. The normal pressure profile for the truncated potential is constant through the interface and both vapor and liquid regions only when this contribution is taken into account, and ignoring it results in incorrect value of surface tension.
Chemical Physics, 2007
Isotherms of experimental data of internal pressure of dense fluids versus molar volume, V m are shown to have each a maximum point at a V max below the critical molar volume. In this study, we investigated the role of attractive and repulsive intermolecular energies on this behavior using a molecular dynamics simulation technique. In the simulation, we choose the Lennard-Jones (LJ) intermolecular potential energy function. The LJ potential is known to be an effective potential representing a statistical average of the true pair and many-body interactions in simple molecular systems. The LJ potential function is divided into attractive and repulsive parts. MD calculations have produced internal energy, potential energy, transitional kinetic energy, and radial distribution function (RDF) for argon at 180 K and 450 K using LJ potential, LJ repulsive, and LJ attractive parts. It is shown that the LJ potential function is well capable of predicting the inflection point in the internal energy-molar volume curve as well as maximum point in the internal pressure-molar volume curve. It is also shown that at molar volumes higher than V max , the attractive forces have strong influence on determination of internal energy and internal pressure. At volumes lower than V max , neither repulsive nor attractive forces are dominating. Also, the coincidence between RDFs resulting from LJ potential and repulsive parts of LJ potential improves as molar volume approaches V max from high molar volumes. The coincidence becomes complete at Vmax >,= V.
Journal of Colloid and Interface Science, 1997
same theory against more complex mixtures such as CS 2 / We report a study of the surface tension of three binary liquid CH 2 Cl 2 and CS 2 / CCl 4 ; the authors found out that by fitting mixtures of molecular fluids. A microscopic mean field theory the energy parameters (e) of the pure components and one (MFT) has been used to calculate the theoretical results enabling binary parameter to the surface tension, the theory could the comparison with the experimental data. The mean field theory explain the qualitative differences between the two systems.
The Journal of Chemical Physics, 2004
A Helmholtz free energy density functional is developed to describe the vapor-liquid interface of associating chain molecules. The functional is based on the statistical associating fluid theory with attractive potentials of variable range ͑SAFT-VR͒ for the homogenous fluid ͓A. , J. Chem. Phys. 106, 4168 ͑1997͔͒. A standard perturbative density functional theory ͑DFT͒ is constructed by partitioning the free energy density into a reference term ͑which incorporates all of the short-range interactions, and is treated locally͒ and an attractive perturbation ͑which incorporates the long-range dispersion interactions͒. In our previous work ͓F. J. Blas, E. Martín del Río, E. de Miguel, and G. Jackson, Mol. Phys. 99, 1851 ͑2001͒; G. J. Gloor, F. J. Blas, E. Martín del Río, E. de Miguel, and G. Jackson, Fluid Phase Equil. 194, 521 ͑2002͔͒ we used a mean-field version of the theory ͑SAFT-HS͒ in which the pair correlations were neglected in the attractive term. This provides only a qualitative description of the vapor-liquid interface, due to the inadequate mean-field treatment of the vapor-liquid equilibria. Two different approaches are used to include the correlations in the attractive term: in the first, the free energy of the homogeneous fluid is partitioned such that the effect of correlations are incorporated in the local reference term; in the second, a density averaged correlation function is incorporated into the perturbative term in a similar way to that proposed by Toxvaerd ͓S. Toxvaerd, J. Chem. Phys. 64, 2863 ͑1976͔͒. The latter is found to provide the most accurate description of the vapor-liquid surface tension on comparison with new simulation data for a square-well fluid of variable range. The SAFT-VR DFT is used to examine the effect of molecular chain length and association on the surface tension. Different association schemes ͑dimerization, straight and branched chain formation, and network structures͒ are examined separately. The surface tension of the associating fluid is found to be bounded between the nonassociating and fully associated limits ͑both of which correspond to equivalent nonassociating systems͒. The temperature dependence of the surface tension is found to depend strongly on the balance between the strength and range of the association, and on the particular association scheme. In the case of a system with a strong but very localized association interaction, the surface tension exhibits the characteristic ''s shaped'' behavior with temperature observed in fluids such as water and alkanols. The various types of curves observed in real substances can be reproduced by the theory. It is very gratifying that a DFT based on SAFT-VR free energy can provide an accurate quantitative description of the surface tension of both the model and experimental systems.
The Journal of Chemical Physics, 2002
We use molecular dynamics simulations of particles interacting through a truncated Lennard-Jones potential to study the surface properties of the curved liquid–vapor interface. We determine the Tolman length δ, investigate its critical behavior, and provide first results for the rigidity constants of bending, k, and of Gaussian curvature, k̄. The rigidity constant of bending, determined at three different temperatures, is found to be positive and of the order of one-half kBT. The rigidity constant of Gaussian curvature, determined at a single temperature, is of the same order of magnitude.
A critical study of simulations of the Lennard-Jones liquid-vapor interface
Fluid Phase Equilibria, 1992
The surface tension and li and two-component Lennard-P uid-gas density profile through the interface of oneits simulation techniques. ones fluids were calculated using Molecular Dynam-The system size, film thickness, interface area, intermolecular potential cut-off, composition, and temperature were varied. For the onecomponent system, the results were compared to previous work and some discreancies of the past work were resolved. By combining this work with correct resu ts P from and t R revious authors, the minimum system size, film thickness, equilibration time, e trade-off between cut-off and corn uter time were determined. Using configurations calculated for moderate cut-o ffp s, the surface tension was extrapolated to the full potential value by using a tail correction and the results compared to simulations performed with the longer cut-offs. The results showed the possibility of obtaining estimates of the surface tension for large cut-off simulattons from moderate cut-off simulations provided that the density profile does not change significantly with increase in cut-off. Using the cntenon for equrhbratron determined from the one-component systems, two-component systems at varying compositions and temperatures were simulated and the tail correction applied.
Physical Review E, 2007
simulations have been performed to study the interfacial properties of the liquid-vapor interface of alkanes. We highlight the chemical equilibrium of the liquid-vapor interface by calculating a local chemical potential including the appropriate long-range corrections profiles. We extend the "test-area" ͑TA͒ technique developed by Gloor et al. ͓J. Chem. Phys. 123, 134703 ͑2005͔͒ on Lennard-Jones and square-well fluids to molecular systems. We establish both operational expressions of the TA approach for the calculation of the surface tension profile and the corresponding long-range corrections by underlining the approximations used. We compare the results between the different operational expressions of the surface tension and focus on the truncation procedures to explain the difference between the different techniques using either the potential or force equations. We make the results of surface tension identical between the different methods by using consistent potential and force equations. In the case of a relatively small cutoff, we propose to show that the Irving-Kirkwood definition and TA methods lead to the same value of the surface tension under condition that appropriate long-range corrections be included in the calculation. We end this paper by calculation of the entropy change profile and a comparison with experiments.
A molecular theory of liquid interfaces
Physical Chemistry Chemical Physics, 2005
We propose a site-site generalization of the Lovett-Mow-Buff-Wertheim integro-differential equation for the one-particle density distributions to polyatomic fluids. The method provides microscopic description of liquid interfaces of molecular fluids and solutions. It uses the inhomogeneous site-site direct correlation function of molecular fluid consistently constructed by nonlinear interpolation between the homogeneous ones. The site-site correlations of the coexisting bulk phases are obtained from the reference interaction site model (RISM) integral equation with our closure approximation. For illustration, we calculated the structure of the planar liquid-vapor as well as liquid-liquid interfaces of n-hexane and methanol at ambient conditions.