An intermolecular potential for hydrogen: Classical molecular simulation of pressure-density-temperature behavior, vapor-liquid equilibria, and critical and triple point properties.

An intermolecular potential is reported for molecular hydrogen that combines two-body interactions from ab initio data with three-body interactions. The accuracy of the two-body potential is validated by comparison with experimental second virial coefficient data. Experimental pressure-density-temperature data are used to validate the addition of three-body interactions, often yielding very accurate predictions.

Accurate determination of solid-liquid equilibria by molecular simulation: Behavior of Ne, Ar, Kr, and Xe from low to high pressures.

We report the accurate determination of solid-liquid equilibria using a novel molecular simulation method that can be used for solid-liquid equilibria from low to high pressures. A re-evaluation is reported of the solid-liquid equilibria of the noble gases interacting via ab initio two-body potentials combined with three-body interactions and quantum corrections and the results are compared with both existing simulation data and experimental values. The new simulation method yields results that are generally in closer agreement with the experiment than exiting methods, highlighting the important role of the method in fully understanding the interatomic interactions responsible for solid-liquid equilibria.

First-principles determination of the solid-liquid-vapor triple point: The noble gases.

We report first-principles calculations of the triple point that allow us to predict the triple point temperature of atomic fluids to an accuracy that has not been previously possible. This is achieved by proposing a molecular simulation technique that can be used for solid-liquid equilibria at arbitrarily low pressures. It is demonstrated that the triple point is significantly influenced by the choice of two-body, three-body and quantum interactions.

Structure and Contact Angle in Sessile Droplets of Binary Mixtures of Lennard-Jones Chains: A Molecular Dynamics Study.

Molecular dynamics simulations were carried out to investigate cylindrical droplets consisting of binary mixtures of Lennard-Jones (LJ) fluids in contact with a solid substrate. The droplets are composed of mixtures of the monomeric LJ fluid plus linear-tangent chains of 2, 10, 20, and 30 segments per chain that interact through a harmonic potential and the spherically truncated and shifted potential Lennard-Jones. The solid surface was modeled as a semi-infinite platinum substrate with an FCC structure that interacts with the fluid by means of a LJ 9-3 potential.

Interatomic Interactions Responsible for the Solid-Liquid and Vapor-Liquid Phase Equilibria of Neon.

The role of interatomic interactions on the solid-liquid and vapor-liquid equilibria of neon is investigated via molecular simulation using a combination of two-body , three-body, and quantum potentials. A new molecular simulation approach for determining phase equilibria is also reported and a comparison is made with the available experimental data. The combination of two-body plus quantum influences has the greatest overall impact on the accuracy of the prediction of solid-liquid equilibria.

Interfacial properties of binary mixtures of Lennard-Jones chains in planar interfaces by molecular dynamics simulation.

Binary mixtures of fully flexible linear tangent chains composed of bonded Lennard-Jones interaction sites (monomers) were studied using the molecular dynamics simulation in the NVT ensemble. Their interfacial properties were investigated in planar interfaces by direct simulation of an explicit liquid film in equilibrium with its vapor. A method for the calculation of long-range interactions in inhomogeneous fluids was implemented to take into account the potential truncation effects.

Characteristic Curves of the Lennard-Jones Fluid.

Equations of state based on intermolecular potentials are often developed about the Lennard-Jones (LJ) potential. Many of such EOS have been proposed in the past. In this work, 20 LJ EOS were examined regarding their performance on Brown's characteristic curves and characteristic state points.

Ab Initio Interatomic Potentials and the Classical Molecular Simulation Prediction of the Thermophysical Properties of Helium.

The ability of modern ab initio potentials to predict the thermophysical properties of helium is investigated. A new interatomic potential for helium is reported that is based on the latest available ab initio data and that is much more computationally efficient than other ab initio potentials, without sacrificing accuracy. The role of both two-body and three-body interactions is evaluated using classical Monte Carlo and molecular dynamics simulations.

Fully a priori prediction of the vapor-liquid equilibria of Ar, Kr, and Xe from ab initio two-body plus three-body interatomic potentials.

Fully a priori predictions are reported for the vapor-liquid equilibria (VLE) properties of Ar, Kr, and Xe using molecular simulation techniques and recently developed ab initio two-body interatomic potentials. Simulation data are reported at temperatures from near the triple point to close to the critical point. The two-body ab initio potentials exaggerate the size of the experimental VLE temperature-density envelope, overestimating the critical temperature and underestimating the vapor pressure.

Two-body interatomic potentials for He, Ne, Ar, Kr, and Xe from ab initio data.

A new method is reported for developing accurate two-body interatomic potentials from existing ab initio data. The method avoids the computational complexity of alternative methods without sacrificing accuracy. Two-body potentials are developed for He, Ne, Ar, Kr, and Xe, which accurately reproduce the potential energy at all inter-atomic separations.

Calculation of phase envelopes of fluid mixtures through parametric marching.

Two-dimensional cross-sections of the phase envelopes of fluid mixtures-in particular isotherms, isobars, and isopleths-are often computed point-by-point by incrementing a so-called marching variable and solving the equilibrium conditions at each step. The marching variable is usually pressure, temperature, or a mole fraction, depending on the application. These isolines, however, can have rather complicated shapes, so that a simple unidirectional "sweep" of the marching variable often gives merely a part of the desired isoline.

Determination of the Residual Entropy of Simple Mixtures by Monte Carlo Simulation.

Extensive Monte Carlo simulations were performed for (neon + krypton) mixtures for temperatures between 200 K and 600 K and pressures up to 1 GPa, using Lennard-Jones potentials to describe the intermolecular interactions. The residual entropies were obtained via Widom's insertion method, as well as via an integration technique. At high pressures, the residual entropy is, to a very good approximation, a linear function of λ, which is the reciprocal value of the average Monte Carlo displacement parameter that gives the acceptance ratio a for translational moves.

Unphysical Critical Curves of Binary Mixtures Predicted with GERG Models.

When applied to asymmetric binary mixtures (e.g., methane + pentane or heavier alkanes, hydrogen-containing mixtures), the GERG equation of state (GERG-2004 or GERG-2008) predicts critical curves with physically unreasonable temperature maxima above the critical temperature of the heavier component.

Calculating thermodynamic properties of an ionic liquid with Monte Carlo simulations with an orthorhombic and a cubic simulation box.

In contrast to the common usage of cubic simulation boxes, in this work simulations of the ionic liquid 1-n-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF(6)]) were carried out in a dynamic orthorhombic simulation box over a temperature range from 313 to 373 K in a canonical harmonical simulation ensemble (NpT) with a united-atom potential based on quantum chemistry. The solubilities of the gases CO(2), CO, H(2), O(2), C(2)H(4), and H(2)O at infinite dilution were determined by means of the Widom test particle method; the results are compared with experimental data and simulation results obtained with a cubic simulation box. For gas potentials containing partial charges the results are in good agreement with the experimental data.

Generalization of the friction theory for viscosity modeling.

The friction theory (FT) approach relates the viscosity of a fluid to its equation of state (EoS), and it is known to give good results for a large number of compounds over wide ranges of temperature and pressure. Previous FT versions were restricted to use EoS of the van der Waals type, i.e.