New Closed Virial Equation of State for Hard-Sphere Fluids

New equations of state for the hard polyhedron fluids

In this paper, we derived a new equation of state for hard polyhedron fluids that is obtained by the knowledge of virial coefficients and a fit to the computer simulation data for the compressibility factor, and which contains two adjustable parameters. This equation reproduces exactly the correct known virial coefficients up to the ninth one and also the compressibility factor data with high accuracy, the absolute average deviations (AADs) being 0.05% for the stable state and 1.12% for both stable and metastable states for the hard tetrahedron fluid. For 12 of the other hard polyhedron fluids, it reproduces exactly the correct known virial coefficients up to the eighth one and also the compressibility factor data in the stable state with AADs less than 0.25%, with the only exception being the triangular prism polyhedron fluid.

Equations of the state of hard sphere fluids based on recent accurate virial coefficients B5–B12

A review on the numerical virial coefficients, compressibility factor, fluid–solid phase transition point and equations of the state of hard sphere fluids.

Fifth to eleventh virial coefficients of hard spheres

Virial coefficients B(n) of three-dimensional hard spheres are reported for n=5 to 11, with precision exceeding that presently available in the literature. Calculations are performed using the recursive method due to Wheatley, and a binning approach is proposed to allow more flexibility in where computational effort is directed in the calculations. We highlight the difficulty as a general measure that quantifies performance of an algorithm that computes a stochastic average and show how it can be used as the basis for optimizing such calculations.

Calculation of high-order virial coefficients with applications to hard and soft spheres

A virial expansion of fluid pressure in powers of the density can be used to calculate a wealth of thermodynamic information, but the Nth virial coefficient, which multiplies the Nth power of the density in the expansion, becomes rapidly more complicated with increasing N. This Letter shows that the Nth virial coefficient can be calculated using a method that scales exponentially with N in computer time and memory. This is orders of magnitude more efficient than any existing method for large N, and the method is simple and general. New results are presented for N = 11 and 12 for hard spheres, and N = 9 and 10 for soft spheres.

An asymptotically consistent approximant method with application to soft- and hard-sphere fluids

A modified Padé approximant is used to construct an equation of state, which has the same large-density asymptotic behavior as the model fluid being described, while still retaining the low-density behavior of the virial equation of state (virial series). Within this framework, all sequences of rational functions that are analytic in the physical domain converge to the correct behavior at the same rate, eliminating the ambiguity of choosing the correct form of Padé approximant. The method is applied to fluids composed of "soft" spherical particles with separation distance r interacting through an inverse-power pair potential, φ = ε(σ∕r)(n), where ε and σ are model parameters and n is the "hardness" of the spheres. For n < 9, the approximants provide a significant improvement over the 8-term virial series, when compared against molecular simulation data. For n ≥ 9, both the approximants and the 8-term virial series give an accurate description of the fluid behavior, when compared with simulation data. When taking the limit as n → ∞, an equation of state for hard spheres is obtained, which is closer to simulation data than the 10-term virial series for hard spheres, and is comparable in accuracy to other recently proposed equations of state. By applying a least square fit to the approximants, we obtain a general and accurate soft-sphere equation of state as a function of n, valid over the full range of density in the fluid phase.