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Collective excitations in hard-sphere fluids were studied in a wide range of wave numbers and packing fractions η by means of molecular dynamics simulations. We report the observation of non-hydrodynamic transverse excitations for packing fractions η ≥ 0.395 in the shape of transverse current spectral functions. Dispersion of longitudinal excitations in the whole range of packing fractions shows a negative deviation from the linear hydrodynamic law with increasing wave numbers even for dense hard-sphere fluids where the transverse excitations were observed. These results do not support a recent proposal within the "Frenkel line" approach that the positive sound dispersion in liquids is defined by transverse excitations. We report calculations of the cutoff "Frenkel frequencies" for transverse excitations in hard-sphere fluids and discuss their consistency with the estimated dispersions of shear waves. [ABSTRACT FROM AUTHOR]

We consider the applicability of coarse-grained molecular dynamics for the simulation of defects in a nematic liquid crystal around a colloidal particle. Two types of colloids are considered, a soft colloid resembling a liquid crystal dendrimer or a similar macromolecule. In addition, a decorated colloid is used which could represent a gold nanoparticle with mesogen-modified surface. For both models we consider homeotropic and tangential anchoring. Precise control of the easy axis on the colloid's surface enables us to focus on specific planar arrangements in the case of a decorated colloid. The nematic phase is modelled explicitly via soft spherocylinders interacting through a potential, suggested by Lintuvuori and Wilson [J. Chem. Phys.128, 044906 (2008)]. Properties of the nematic phase are studied by computing the Frank elastic constants. In addition, estimates for the nematic-isotropic transition and the coherence length allow us to establish a relation between energy and length scales with respect to experimental systems. Both models exhibit similar defect topologies, namely, that of a Saturn ring and a boojum-type of defect for homeotropic and tangential surface anchoring, respectively. In the decorated colloid model we tune the anchoring strength through the density of the mesogenic shell on the surface. We also found the biaxial boojum defect for the special case of longitudinal planar anchoring. The study demonstrates the potential of coarse-grained simulation methods for studying defects in liquid crystals. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation study of the vapor-liquid coexistence in two-dimensional square-well fluid with 12 different values of the attraction shell width are reported. The densities of coexisting vapor and liquid phases as well as the coexisting chemical potentials for each simulated system are determined by means of hyperparallel tempering and histogram reweighting technique, while the location of critical point was tuned by means of the finite size scaling analysis. By studying dependence of the critical point parameters on the attraction shell width, we found that critical point temperature and critical point chemical potential both are changing monotonically while the critical point density oscillates, exhibiting higher or lower values depending on the particular width of the attraction shell. [ABSTRACT FROM AUTHOR]

The direct correlation function of the complex discrete potential model fluids is obtained as a linear combination of the first-order mean spherical approximation (FMSA) solution for the simple square well model that has been reported recently [Hlushak et al., J. Chem. Phys. 130, 234511 (2009)]. The theory is employed to evaluate the structure and thermodynamics of complex fluids based on the square well-barrier and square well-barrier-well discrete potential models. Obtained results are compared with theoretical predictions of the hybrid mean spherical approximation, already reported in the literature [Guillen-Escamilla et al., J. Phys.: Condens. Matter 19, 086224 (2007)], and with computer simulation data of this study. The compressibility route to thermodynamics is then used to check whether the FMSA theory is able to predict multiple fluid-fluid transitions for the square barrier-well model fluids. [ABSTRACT FROM AUTHOR]

A two-Yukawa representation of the EXP6 fluids at supercritical temperatures and high pressures has been developed and examined using molecular simulations. A uniquely defined mapping of the repulsive part of the EXP6 potential curve onto the two-Yukawa potential is used. Two ranges of temperatures, one encountered in geochemical applications (Tgeo range) and the other at conditions of detonations (Tdet range), are considered and it is shown that the local structures of both fluids are practically identical. Deviations between the EXP6 and two-Yukawa potential functions at intermediate separations lead to differences in the thermodynamic properties of the two fluids at lower temperatures of the Tgeo range; at higher temperatures and in the high Tdet temperature range both the structural and thermodynamic properties of the EXP6 and two-Yukawa fluids are practically identical. [ABSTRACT FROM AUTHOR]

The liquid-vapor phase diagram and surface tension for the Sutherland fluids with a variable range of interaction have been determined by canonical Monte Carlo simulations and compared with the augmented van der Waals analytic theory. The theory, based on a short-range Yukawa reference, performs well for medium-range models but its accuracy deteriorates with the shortening range due to deteriorating accuracy of the underlined analytic mean spherical approximation solution for the reference Yukawa potential. The simulation results are also analyzed from the point of the extended principle of corresponding states and it is shown that the surface tension and also, to a certain degree of accuracy, the vapor-liquid coexistence curve satisfy the principle. [ABSTRACT FROM AUTHOR]

Analytical expression for direct correlation function of the square-well fluid with an attractive well width up to two particle diameters (2≤λ≤3) is reported. This result is obtained within the first-order mean-spherical approximation (FMSA) and represents the nontrivial extension of the recent study due to Tang [J. Chem. Phys. 127, 164504 (2007)], where the width of square-well attraction was limited by one particle diameter (1≤λ≤2). Prediction of the FMSA theory is validated by direct comparison against Monte Carlo simulation data. Additionally, an impact of the increase in the range of attraction on the parameters of the critical point of the square-well fluid is discussed using the compressibility route to thermodynamics [ABSTRACT FROM AUTHOR]

A novel perturbation approach for the structure factor S(k) of the Lennard-Jones-type Yukawa fluid with z=1.8 is presented. An approach is based on a new reference system, that is, the short-range Yukawa model with z0>z=1.8. By choosing for the reference system the value z0=6, it is shown that (i) the proposed approach for S(k) performs much better than the traditional hard-sphere reference perturbation method does; (ii) the use of an approximate mean spherical (MSA) description of the reference structure factor provides the results for S(k) that are more accurate as those obtained from the direct MSA computations; and (iii) the results obtained for S(k) tend to reproduce “exact” simulation results when accurate simulation data for the reference system are used. [ABSTRACT FROM AUTHOR]

A theoretically based closed-form analytical equation for the radial distribution function, g(r), of a fluid of hard spheres is presented and used to obtain an accurate analytic representation. The method makes use of an analytic expression for the short- and long-range behaviors of g(r), both obtained from the Percus-Yevick equation, in combination with the thermodynamic consistency constraint. Physical arguments then leave only three parameters in the equation of g(r) that are to be solved numerically, whereas all remaining ones are taken from the analytical solution of the Percus-Yevick equation. [ABSTRACT FROM AUTHOR]

Monte Carlo simulation techniques were employed to explore the effect of short-range attraction on the orientational ordering in a two-dimensional assembly of monodisperse spherical particles. We find that if the range of square-well attraction is approximately 15% of the particle diameter, the dense attractive fluid shows the same ordering behavior as the same density fluid composed of purely repulsive hard spheres. Fluids with an attraction range larger than 15% show an enhanced tendency to crystallization, while disorder occurs for fluids with an attractive range shorter than 15% of the particle diameter. A possible link with the existence of “repulsive” and “attractive” states in dense colloidal systems is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An approach to study the effective interaction between two extremely large spheres, infinitely dilute, in a multicomponent hard-sphere fluid is presented. The proposed approach is an approximation that guarantees at least qualitative consistency with the experimental results for the interaction between two large solutes that is mediated by a background medium. The approach is developed to study the complex colloidal systems, i.e., extremely large (micronsized) spherical particles immersed in suspensions of the smaller (nanosized) colloid particles that are dissolved in a molecular solvents. Numerical results for the effective energy and force between two extremely large spheres in a one-component hard-sphere fluid (when only colloid particles are considered explicitly) and a two-component hard-sphere fluid (when both “solvent” particles and colloid particles are considered explicitly), are presented. The role of the discrete nature of the solvent on the interaction between two extremely large spheres immersed in a colloidal suspension is discussed. To account for the effect of colloid particle size polydispersity, calculations with four-component and ten-component hard-sphere fluids are performed. Using the Derjaguin approximation, the disjoining energy and pressure between two flat hard surfaces separated by a multicomponent hard-sphere fluid could be obtained. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on canonical molecular dynamics (MD) and Monte Carlo (MC) simulations for liquid/vapor equilibrium in truncated Lennard-Jones fluid. Reason for differences in results for coexistence properties; Use of truncated potentials in MC calculations and truncated forces for MD calculations.

Studies the associative replica Ornstein-Zernike equations and the structure of chemically reacting fluids in porous media. Constructing the model for associating fluids in disordered porous media; Temperature changes of the distribution functions for the dimerizing model for the case of low and high fluid densities.

The linear response theory is applied to the interaction site model for the evaluation of static dielectric properties of a flexible water model. The atom–atom radial distribution functions derived from hybridization of the computer simulations and optimized cluster theory [A. D. Trokhymchuk, M. F. Holovko, E. Spohr, and K. Heinzinger, Mol. Phys. 77, 903 (1992)] are employed for the calculation of the polarization structure factor and the moments of the polarization correlation function. The color charge version of the dipolar hard sphere model [F. O. Raineri, H. Resat, and H. L. Friedman, J. Chem. Phys. 96, 3068 (1992)] proved to be helpful for the understanding of the effects of intramolecular charge distribution and flexibility on the dielectric properties of the interaction site model. The dielectric constant for the flexible BJH water model is calculated and the region of negative values of the static dielectric function is obtained. The possibility of a subdivision of this region into two parts at k about 1–2 Å-1 is pointed out. [ABSTRACT FROM AUTHOR]

Examines the density profiles of the liquid-vapor interface of Lennard-Jones fluid in porous media using hard sphere rigid matrix based on Born-Green-Yvon equation. Comparison of results with Monte Carlo simulations; Increase of interface thickness in disordered media; Evaluation of phase diagram for different matrix densities.

Discusses the application of the replica Ornstein-Zernike equations for an ionic fluid adsobred in an electroneutral, disordered matrix of ions, to a model where both ionic subsystems as point charges interacting only via Coulomb forces. Effects of fluid and matrix concentration on the screening of the ion-ion interactions in the fluid phase.

The adsorption of associating hard spheres on a hard wall by using the nonuniform Percus–Yevick equation for the local density and the pair correlation functions is studied. A comparison of the density profiles with computer simulation data indicates that this approximation predicts the fluid structure significantly better than the singlet Percus–Yevick and hypernetted chain approximations. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The theory, which utilizes an exponential enhancement of the first-order mean spherical approximation (FMSA) for the radial distribution functions of the hard-core plus square-well fluid, is adopted to study the properties of the simplest model of the core-softened fluids, i.e., the hard spheres with a square-shoulder interaction. The results for structure and thermodynamic properties are reported and compared against both the Monte Carlo simulation data as well as with those obtained within the conventional FMSA theory. We found that in the region of low densities and low temperatures, where the conventional FMSA theory fails, the exponential-based FMSA theory besides being qualitatively correct also provides with a notable quantitative improvement of the theoretical description. [ABSTRACT FROM AUTHOR]

A correction to the article "Hard Sphere Radial Distribution Function Again," by Andrij Trokhymchuk, Ivo Nezbeda, Jan Jirsák and Douglas Henderson that was published in the 2005 issue is presented.

Canonical ensemble molecular dynamics and Monte Carlo simulations have been performed to study the vapor/liquid coexistence in a hard-core fluid with an attractive Yukawa interaction. Coexisting densities and pressure along the vapor/liquid coexistence line for different ranges of attractive interaction have been evaluated and found to agree well with the Gibbs ensemble Monte Carlo data reported in the literature. To obtain surface tension, the normal and tangential components of the pressure tensor have been calculated during simulations by using a hybrid molecular dynamics algorithm (which combines the hard-core and continuous forces) and by using an original numerical algorithm for the hard-core contribution to the virial in Monte Carlo simulations. We found that surface tension is strongly dependent on the range of attractive interaction, i.e., it drops when the attraction becomes short-ranged. The relation of the attractive hard-core Yukawa potential to the spherically-truncated Lennard-Jones potential in terms of the interfacial properties is discussed. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]