Virial coefficients and equation of state of the penetrable sphere model.

We study the penetrable sphere (alias square mound) model in the fluid phase by means of the virial expansion, molecular dynamics simulations, and Ornstein-Zernike integral equation. The virial coefficients up to B(8) are expressed as polynomials in the Boltzmann factor with the coefficients calculated by a Monte Carlo integration. New data for pressure and internal energy are obtained by molecular dynamics simulations with attention paid to finite-size errors and properties of the Andersen thermostat.

Optimized equation of the state of the square-well fluid of variable range based on a fourth-order free-energy expansion.

The free energy of square-well (SW) systems of hard-core diameter sigma with ranges 1 < or = lambda < or = 3 is expanded in a perturbation series. This interval covers most ranges of interest, from short-ranged SW fluids (lambda approximately 1.2) used in modeling colloids to long ranges (lambda approximately 3) where the van der Waals classic approximation holds.

Virial coefficients of hard spheres and hard disks up to the ninth.

A technique for topological analysis of the Ree-Hoover diagrams is developed with the aim to calculate the Ree-Hoover weights up to the ninth order with moderate demands on computer storage and CPU time. The ninth virial coefficients of hard spheres and disks are calculated, and the lower virial coefficients are accurately recalculated. The calculations require several spanning diagrams; the most important spanning chains are generated by reptation, other spanning diagrams by the standard Metropolis Monte Carlo algorithm.

Structure of ternary additive hard-sphere fluid mixtures.

Monte Carlo simulations on the structural properties of ternary fluid mixtures of additive hard spheres are reported. The results are compared with those obtained from a recent analytical approximation [S. B.