Molecular simulation of the phase behavior of noble gases using accurate two-body and three-body intermolecular potentials

Gibbs ensemble Monte Carlo simulations are reported for the vapor- liquid phase coexistence of argon, krypton, and xenon. The calculations employ accurate two-body potentials in addition to contributions from three-body dispersion interactions resulting from third-order triple-dipole, dipole-dipole-quadrupole, dipole- quadrupole-quadrupole, quadrupole-quadrupole-quadrupole, and fourth- order triple- dipole terms. It is shown that vapor-liquid equilibria are affected substantially by three-body interactions. The addition of three-body interactions results in good overall agreement of theory with experimental data. In particular, the subcritical liquid- phase densities are predicted accurately. (C) 1999 American Institute of Physics. S0021- 9606(99)50728-9

The Dieterici alternative to the van der Waals approach for equations of state: second virial coefficients

Historically, the development of equations of state for fluids has almost invariably followed the lead of the van der Waals equation by simply adding together contributions from intermolecular repulsion and attraction. Recently an alternative approach, first suggested by Dieterici (Ann. Phys. Chem. Wiedemanns Ann.,1899, 69, 685), has been revised (R. J. Sadus, J. Chem. Phys., 2001, 115, 1460) with the benefit of modern developments in equations of state. In contrast to the traditional van der Waals-type equations of state, the Dieterici approach results in an equation of state that is the product of a repulsive term with an exponential attractive term. This formulation significantly enhances the accuracy of the prediction of vapour–liquid equilibria, particularly in the vicinity of the critical point. In this work, the ability of the equation to predict second virial coefficients is investigated. A comparison is also reported with traditional van der Waals-type equations of state. The results indicate that the Dieterici approach yields superior prediction of the second virial coefficients

Simple equation of state for hard-sphere chains

A simplified thermodynamic perturbation theory-dimer framework is used to derive an equation of state for hard-sphere chains. The accuracy of the equation is tested against simulation data for hard-sphere chains containing up to 201 hard-sphere segments. A comparison is also presented with the results of other more sophisticated hard-sphere chain equations of state. The equation reproduces the compressibility factor of hard-sphere chains obtained from molecular simulation with a reasonable degree of accuracy. The equation can potentially form the theoretical backbone of an equation of state for real chainlike molecules. From a practical perspective, it has the advantage of being considerably simpler than alternative hard-sphere chain equations. A simplified thermodynamic perturbation theory-dimer framework is used to derive an equation of state for hard-sphere chains. The accuracy of the equation is tested against simulation data for hard-sphere chains containing up to 201 hard-sphere segments. A comparison is also presented with the results of other more sophisticated hard-sphere chain equations of state. The equation reproduces the compressibility factor of hard-sphere chains obtained from molecular simulation with a reasonable degree of accuracy. The equation can potentially form the theoretical backbone of an equation of state for real chainlike molecules. From a practical perspective, it has the advantage of being considerably simpler than alternative hard-sphere chain equations

Molecular simulation and theory for nanosystems: insights for molecular motors

Knowledge of self-assembling molecules such as deoxyribonucleic acid (DNA) and dendritic systems can provide beneficial insights for the development of tailor-made nano-scale devices. Another important category of nanosystems is molecular systems that provide a mechanism of molecular propulsion such a myosin, kinesin and adenosine triphosphate synthase (ATPase). Work on these so-called 'molecular motors' has been led largely by experimental investigations. The application of rigorous theoretical techniques such as molecular simulation is a considerable computational challenge. However, the reward for accepting the challenge can be a greatly improved theoretical insight, which benefits the development of nanotechnologies. In this work, we discuss recent progress in improving the theoretical understanding of an important molecular motor, ATPase

Molecular simulation of the thermophysical properties of fluids : phase behaviour and transport properties

Historically, reliable data for the thermophysical properties of fluids could only be obtained from accurate experimental measurement. The input from theory was, at best, limited to a supporting role by providing correlations. The large number of assumptions and approximations involved in theoretical tools such as equations of state meant that it was unrealistic to expect genuinely reliable predictions. More recently, the advent of powerful molecular simulation techniques has greatly enhanced the usefulness of thermophysical calculations, particularly in chemical engineering. Unlike conventional calculations, molecular simulation determines the properties of a fluid directly by evolving molecular coordinates in accordance with a rigorous calculation of intermolecular energies or forces. In this work, the application of molecular simulation to the prediction of the thermophysical properties of fluids relevant to chemical engineering applications is examined. In particular, the role of three-body interactions on the vapour-liquid coexistence of fluids is illustrated and compared with experimental data. Molecular simulation is also used to compare the viscosities of dendrimer fluids with linear polymers of equivalent molecular weight

Molecular simulation of the phase behaviour of ternary fluid mixtures: the effect of a third component on vapour-liquid and liquid-liquid coexistence

The Gibbs ensemble algorithm is implemented to determine the vapour- liquid and liquid-liquid phase coexistence of dilute ternary fluid mixtures interacting via a Lennard-Jones potential. Calculations are reported for mixtures with a third component characterised by different intermolecular potential energy parameters. Comparison with binary mixture data indicates that the choice of energy parameter for the third component affects the composition range of vapour-liquid substantially. The addition of a third component lowers the energy of liquid phase while slightly increasing the energy of the vapour phase. The Gibbs ensemble algorithm is implemented to determine the vapour-liquid and liquid-liquid phase coexistence of dilute ternary fluid mixtures interacting via a Lennard-Jones potential. Calculations are reported for mixtures with a third component characterized by different intermolecular potential energy parameters. Comparison with binary mixture data indicates that the choice of energy parameter for the third component affects the composition range of vapour-liquid substantially. The addition of a third component lowers the energy of liquid phase while slightly increasing the energy of the vapour phase

Predicting the behaviour of fluids: from atoms tom macromolecules

Abstract not available

Computational challenges in molecular simulation

Abstract not available

An equation of state for hard convex body chains

The thermodynamic perturbation theory of hard sphere chains is generalized to derive an equation of state for hard convex body chains. The hard convex body chain equation of state contains two parameters that are related directly and rigorously to the geometry of the hard convex body. The compressibility factors and second virial coefficients of chains composed of prolate spherocylinders, oblate spherocylinders and doublecones are calculated and compared with hard sphere chain calculations. The comparison indicates that the nature of the hard convex body has a profound influence on the properties of the chain.

New Dieterici-type equations of state for fluid phase equilibria

The vapour–liquid critical properties of binary mixtures are calculated using conformal solution theory, the one-fluid model, the van der Waals and Carnahan–Starling–van der Waals equations, and a new Dieterici-type equation of state reported recently [J. Chem. Phys. 115 (2001) 371]. Comparisons with experimental data are reported for the critical properties of n-alkane mixtures ranging from methane to n-octane. A common feature of these comparisons is that the new Dieterici-type equation of state yields good prediction of the pressure–temperature critical locus without the need to use arbitrary adjustable parameters in the combining rules for mixture properties. In particular, the Dieterici-type equation correctly predicts the maximum in the pressure–temperature curve. In contrast, the van der Waals-type equations are inaccurate. Dieterici-type equations of state may have a useful rule in the prediction of fluid phase equilibria by reducing the need for adjustable parameters in the combining rules