An approach for directly determining the liquid–vapor phase equilibrium of a model system at any temperature along coexistence line is described. The method relies on transition matrix Monte Carlo ideas developed by Fitzgerald, Picard, and Silver [Europhys. Lett. 46, 282 (1999)]. During simulation attempted transitions between states Markov chain are monitored as opposed to tracking number times visits given state done in conventional simulations. Data collection highly efficient very...

This Brief Report describes an approach for determining the surface tension of a model system that is applicable over entire liquid-vapor coexistence region. At heart method technique properties utilize transition probabilities attempted Monte Carlo moves during grand canonical simulation. Finite-size scaling techniques are implemented to determine infinite from series finite-size simulations. To demonstrate method, Lennard-Jones fluid determined at temperatures ranging triple point critical point.

We report results from a molecular simulation study of the structure and dynamics water near single carbohydrate molecules (glucose, trehalose, sucrose) at 0 30 degrees C. The presence molecule has number significant effects on microscopic dynamics. All three carbohydrates disrupt tetrahedral arrangement proximal restrict their translational rotational mobility. These destructuring slow are result steric constraints imposed by ability to form stable H bonds with water, respectively. induce...

We study the diffusive dynamics of a hard-sphere fluid confined between parallel smooth hard walls. The position-dependent diffusion coefficient normal to walls is larger in regions high local packing density. High density also have largest available volume, consistent with fast diffusivity. Indeed, and global diffusivities as function Widom insertion probability approximately collapse onto master curve. Parallel average are strongly coupled at densities deviate from bulk behavior.

Computer simulations are employed to obtain subcritical isotherms of small finite sized systems inside the coexistence region. For all temperatures considered, ranging from triple point up critical point, gradually developed a sequence sharp discontinuities as system size increased ∼8 ∼21 molecular diameters. smallest sizes, and more so close appeared smooth, resembling continuous van der Waals loop obtained extrapolation an analytic equation state outside As was increased, in chemical...

A new fixed-point charge potential model for water has been developed, targeting the accurate prediction of vapor−liquid coexistence properties over a broad temperature range. The consists Buckingham exponential-6 group at oxygen center and set three point charges. was designed primarily to reproduce coexisting vapor liquid densities, pressures, critical parameters secondarily structure ambient conditions. To obtain an optimum intermolecular parameters, Gibbs ensemble histogram reweighting...

A new model for the n-alkane homologous series has been developed, parametrized to vapor−liquid coexistence properties a range of chain lengths. The utilizes Buckingham exponential-6 potential describe nonbonded interaction energy. Histogram reweighting grand canonical Monte Carlo methods were used determine parameters. reproduces experimental saturated liquid and vapor densities pressures ethane through octane within average absolute deviations 0.5%, 2.1%, 2.2% respectively. Critical...

Many thermodynamic and dynamic properties of water display unusual behavior at low enough temperatures. In a recent study, Yan et al. [Phys. Rev. Lett. 95, 130604 (2005)] identified spherically symmetric two-scale potential that displays many the same anomalous as water. More specifically, for select parametrizations potential, one finds regions where isothermal compression anomalously (i) decreases fluid's structural order, (ii) increases its translational self-diffusivity, (iii) entropy...

Grand canonical histogram-reweighting Monte Carlo simulations were used to obtain the phase behaviour of several binary mixtures. The main goal this work was test predictive capabilities recently developed intermolecular potential models that accurately reproduce pure components. These united-atom potentials utilize exponential-6 functional form for repulsive and dispersion interactions fixed point charges electrostatic interactions. mixtures studied n-pentane—methane, ethane—CO2,...

We study how confining the equilibrium hard-sphere fluid to restrictive one- and two-dimensional channels with smooth interacting walls modifies its structure, dynamics, entropy using molecular dynamics transition-matrix Monte Carlo simulations. Although confinement strongly affects local structuring, relationships between self-diffusivity, excess entropy, average density are, an excellent approximation, independent of channel width or particle-wall interactions. Thus, thermodynamics can be...

Vapor–liquid interfacial tension of square-well (SW) fluids is calculated using three different methods viz., molecular dynamics (MD) with collision-based virial evaluation, Monte Carlo computed by volume perturbation, and Binder’s density-distribution method in conjunction grand-canonical transition-matrix (GC-TMMC). Three values the SW attractive well range parameter were studied: λ=1.5, 1.75, 2.0, respectively. The results from MD GC-TMMC are very good mutual agreement, while...

We conduct a numerical investigation of structural order in the shifted-force Lennard-Jones system by calculating metrics translational and bond-orientational along various paths phase diagram covering equilibrium solid, liquid, vapor states. A series non-equilibrium configurations generated through isochoric quenches, isothermal compressions, energy minimizations are also considered. Simulation results analyzed using an ordering map representation [Torquato et al., Phys. Rev. Lett. 84, 2064...

We examine the performance of several molecular simulation techniques aimed at evaluation surface tension through its thermodynamic definition. For all methods explored, is calculated by approximating change in Helmholtz free energy associated with a interfacial area liquid slab constant particle number, volume, and temperature. The explored fall within three general classes: free-energy perturbation, Bennett acceptance-ratio scheme, expanded ensemble technique. Calculations are performed...

It is known that there are thermodynamic states for which the Gaussian-core fluid displays anomalous properties such as expansion upon isobaric cooling (density anomaly) and increased single-particle mobility isothermal compression (self-diffusivity anomaly). Here, we investigate how temperature density affect its short-range translational structural order, characterized by two-body excess entropy. We find a wide range of conditions order decreases (structural As show, origin anomaly...

Static measures such as density and entropy, which are intimately connected to structure, have featured prominently in modern thinking about the dynamics of liquid state. Here, we explore connections between self-diffusivity, density, excess entropy for two most widely used model "simple" liquids, equilibrium Lennard-Jones square-well fluids, both bulk confined environments. We find that self-diffusivity data fluid can be approximately collapsed onto a single curve (i) versus effective...

We examine the extent to which nanoscale geometric substrate roughness influences contact angle droplets establish on solid surfaces. Free-energy-based Monte Carlo simulation methods are used compute angles and interfacial tensions of a model Lennard-Jones fluid substrates with regular one-dimensional heterogeneities characterized by amplitudes periodicities in 2-25 nm range. focus relatively strong surface that facilitates formation Wenzel droplets. Our results enable us probe validity...

We discuss molecular simulation methods for computing the phase coexistence properties of complex molecules. The strategies that we pursue are histogram-based approaches in which thermodynamic related to relevant probability distributions. first outline grand canonical and isothermal-isobaric directly locating a saturation point at given temperature. In former case, show how reservoir growth expanded ensemble techniques can be used facilitate creation insertion molecules within simulation....

We use molecular simulation to study the wetting behavior of water near flat nonpolar surfaces. The interface potential approach is used capture evolution various interfacial properties over a broad range temperature and substrate strength. Three model substrates are considered: an atomistically detailed face-centered cubic (FCC) lattice, graphite structureless wall. first examine contact angle with strength for conditions ranging from drying complete at select temperatures. A notable...

Monte Carlo simulations were used to calculate water−methane and water−ethane phase equilibria over a wide range of temperatures pressures. Simulations performed from room temperature up near the critical water subatmospheric pressure 3000 bar. The Henry's law constants hydrocarbons in calculated Widom test particle insertions. Gibbs ensemble method was for simulation water-rich hydrocarbon-rich phases at higher Two recently proposed pairwise additive intermolecular potentials that describe...

We study clusters formed by water molecules possessing large enough tetrahedrality with respect to their nearest neighbors. Using Monte Carlo simulation of SPC/E and Voronoi tessellation, we find that regions lower density than the bulk are accretion into exceeding a minimum size. Clusters predominantly linear objects become less compact as they grow until reach size beyond which further is not accompanied decrease. The results suggest formation "icelike" in liquid cooperative.

A novel method, Hamiltonian scaling grand canonical Monte Carlo, has been used to determine the phase behavior of 12 variations modified Buckingham exponential-6 potential. Carlo enables determination thermodynamic properties several related potential models from a single set simulations. The main advantage method is that by appropriate selection chemical and temperature for each Hamiltonian, densities are sampled relevant multiple Hamiltonians, thus increasing simulation efficiency. was...

The phase-switch Monte Carlo method of Wilding and Bruce [Phys. Rev. Lett. 85, 5138 (2000)] is extended to enable calculation solid–liquid phase coexistence for soft potentials. directly accesses information about a system while avoiding simulation the interfacial region. Order parameters are introduced that allow one define path connects liquid crystalline phases. Transition matrix methods employed bias sampling such both phases sampled in rapid efficient manner. Coexistence properties...

We present evidence via molecular simulation that the supercooled fluid states of SPC/E water as well "repulsive" and "attractive" a recently introduced model for colloids with short-ranged attractions are characterized by same functional relationship between self-diffusivity pair correlation function. discuss how this simple connects to an earlier finding temperature dependency fluid's single-particle dynamics tracks its excess entropy (relative ideal gas). The generality observed...