Thermodynamics of strongly-coupled Yukawa systems near the one-component-plasma limit. II. Molecular dynamics simulations

Abstract

Molecular dynamics simulations are employed to study the equilibrium thermodynamics of strongly-coupled systems of particles interacting through the Yukawa potential. Such systems serve, under the Debye-Hückel approximation, as a model for the physical behavior of plasma or colloidal suspensions of charged particulates. The thermodynamics may be characterized in terms of two dimensionless parameters-the ratio κ of the mean interparticle distance to the Debye length, and an approximate measure Γ of the interparticle potential energy in units of the thermal kinetic energy. Employing an accurate representation of infinite periodic boundary conditions, we focus on the regime of weak Debye screening (κ ≲ 1) and strong coupling (Γ ≫ 1). Excess internal energies measured at many points (κ, Γ) are fitted to simple functional forms for the fluid and solid phases, representing extrapolations of the classical one-component plasma (OCP) limit, κ=0. Quantitative expressions for the Helmholtz free energy and the "equation of state" of the Yukawa system-giving the pressure p in terms of κ and Γ-are thus derived, and the freezing/melting curve in the (κ, Γ) plane is traced as the intersection of the fluid and solid free-energy surfaces. © 1994 American Institute of Physics.