Yurko Duda

Surface tension of a square well fluid

We performed Monte Carlo simulations in the canonical ensemble on the liquid–vapor interface of a square well fluid with interaction range of λ=1.5σ. The system contains a liquid slab surrounded by vapor. The surface tension is calculated during simulations by using an original procedure that allows the calculation of the pressure tensor components. The surface tension decreases monotonically with temperature. Coexisting densities and pressure along the liquid–vapor coexistence line have also been obtained and good agreement is found with results calculated from bulk simulations.

Liquid–vapor interface of square-well fluids of variable interaction range

Properties of the liquid-vapor interface of square-well fluids with ranges of interaction lambda=1.5, 2.0, and 3.0 are obtained by Monte Carlo simulations and from square-gradient theories that combine the Carnahan-Starling equation of state for hard spheres with the second and third virial coefficients. The predicted surface tensions show good agreement with the simulation results for lambda=2 and for lambda=3 in a temperature range reasonably close to the critical point, 0.8</=T/T(c)</=0.95. As expected, the surface tension increases with the range of interaction and decreases monotonically with temperature. A comparison between theory and simulation results is also given for the width of the interface and for the coexistence curves for the different interaction ranges.

On the corresponding states law of the Yukawa fluid

We have analyzed the currently available simulation results as well as performed some additional Monte Carlo simulation for the hard-core attractive Yukawa fluid in order to study its corresponding state behavior. We show that the values of reduced surface tension map onto the master curve and a universal equation of state can be obtained in the wide range of the attractive Yukawa tail length after a certain rescaling of the number density. Some comparisons with other nonconformal potentials are presented and discussed.

Some universal trends of the Mie(n,m) fluid thermodynamics

By using canonical Monte Carlo simulation, the liquid-vapor phase diagram, surface tension, interface width, and pressure for the Mie(n,m) model fluids are calculated for six pairs of parameters m and n. It is shown that after certain re-scaling of fluid density the corresponding states rule can be applied for the calculations of the thermodynamic properties of the Mie model fluids, and for some real substances.

Network forming fluids: Integral equations and Monte Carlo simulations

A network forming four-site model associative fluid (with freely located sites) is investigated by means of associative Ornstein–Zernike integral equation theory supplemented by a Percus–Yevick-like closure relation. Since the model exhibits critical behavior, the structure relevant to the gaseous and to the liquid phases are discussed. The properties of network forming systems with different strengths of the site-site attraction are analyzed. This allows us to describe topologically asymmetrical network clusters and branching polymers. It is determined that the critical temperature as well as the critical density become lower with an increasing degree of asymmetry. NVT Monte Carlo simulations for the same model, but with a fixed location of sites, are presented. Theoretical predictions are compared to the simulation results. It is shown that the theory agrees well with the simulations, except for low densities and temperatures, where the simulations predict a well developed waterlike structure with a tet...

Square-well fluid modelling of protein liquid-vapor coexistence

The liquid-vapor phase diagrams for square-well fluid with extremely short attractive well, lambda=1.05 and 1.1, are obtained by means of canonical Monte Carlo simulations. These new results show that the coexistence curves obey the law of corresponding states in the similar form as several proteins do. Besides, the critical packing fraction of gamma-crystalline obtained experimentally is surprisingly close to the critical value of the model fluid with lambda=1.1. Thus, we demonstrate that the phase behavior of protein solutions may be modeled without taking into account an implicit anisotropic patchy character of the interprotein interaction.

Continuum Percolation of the Four-Bonding-Site Associating Fluids

Wertheim’s integral equation theory for associating fluids is reformulated for the study of the connectedness properties of associating hard spheres with four bonding sites. The association interaction is described as a square-well saturable attraction between these sites. The connectedness version of the Ornstein-Zernike (OZ) integral equation is supplemented by the PY-like closure relation and solved analytically within an ideal network approximation in which the network is represented as resulting from the crossing of ideal polymer chains. The pair connectedness functions and the mean cluster size are calculated and discussed. The condition for the percolation transition and the analytical form of the percolation threshold are derived. The connection of the percolation with the gas-liquid phase transition is discussed.

Computer modeling of the liquid–vapor interface of an associating Lennard-Jones fluid

Monte Carlo and molecular dynamics methods have been used to investigate the influence of chemical association on the structure and thermodynamic properties of the liquid–vapor interface of dimerizing Lennard-Jones fluids. The molecular dynamics simulations have been carried out to obtain the surface tension for the so-called pseudo-mixture model of an associating fluid. The simulation data are also compared with the results of theoretical calculations, based on a density functional approach.

Microscopic structure and thermodynamics of a core-softened model fluid: Insights from grand canonical Monte Carlo simulations and integral equations theory

We have studied the microscopic structure and thermodynamic properties of isotropic three-dimensional core-softened model fluid by using extensive grand canonical Monte Carlo computer simulations and Ornstein-Zernike integral equations with hypernetted chain and Rogers-Young closures. Applied simulation tools permit to obtain insights into the properties of the model in addition to available molecular dynamics data of other authors. We discuss equation of state in the density-chemical potential projection and explore the temperature dependence of the chemical potential along different isochores. The limits of the region of anomalous behavior of the structural and thermodynamic properties are established by investigating derivatives resulting from the equation of state, pair contribution to excess entropy, and translational order parameter. Besides, we evaluate the dependence of the heat capacity on temperature and density. The microscopic structure is discussed in terms of the pair distribution functions and corresponding structure factors. We have established that the hypernetted chain approximation is not successful to capture the region of anomalies in contrast to Rogers-Young approximation, but is very accurate for high fluid densities. Thus we have studied the onset for crystallization transition within this theoretical framework. Moreover, using the replicated Ornstein-Zernike integral equations with hypernetted chain closure, we explore the possibility of glass transition and described it in terms of transition density and chemical potential.

Binary system of network-forming fluid: Study of phase stability through an analytical solution of the Percus–Yevick equation

Phase equilibria of a binary mixture of equal-sized network forming fluid (hard sphere diameters D[a]=D[b]) with associative forces between like species and hard sphere repulsion between unlike species are determined using an analytical solution of the associative Percus–Yevick integral equation. The theory shows how occurrence of coexistence lines correlates with the interparticle potential parameters, density and composition of the system. The phase behavior of the system with varying degrees and symmetry of association is studied. Namely, immiscibility curves for the mixture of chains and network-forming fluid are built and discussed.