Nonlinear-response-function approach to binary ionic mixtures: Dynamical theory.

Abstract

The authors generalize the Golden-Kalman one-component-plasma (OCP) nonlinear-response-function approach to the formulation of a dynamical theory for binary-ionic-mixture plasmas. The principal result of the new dynamical theory is a self-consistent approximation scheme for the calculation of linear ionic polarizabilities and collective-mode structure at long wavelengths and arbitrary coupling strengths. The approximation scheme is constructed from the dynamical nonlinear fluctuation-dissipation theorem and the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) kinetic equation prepared in the velocity-average approximation (VAA). Equilibrium three-point correlations, quadratic response functions, and the dynamical superposition approximation are all central elements of the theory. The theory is exact at zero frequency and exactly reproduces the coefficients of the high-frequency-moment-sum-rule expansion through order 1/..omega../sup 4/. Collective-mode calculations based on the new approximation scheme indicate that the (positive) shift in the plasma frequency is temperature dependent at weak coupling and temperature independent at very strong coupling. These calculations, moreover, reproduce the qualitative features of the Hansen-McDonald-Vieillefosse molecular-dynamics data for the dispersion of the optical mode in the strong-coupling regime, while at the same time very nearly reproducing the weak-coupling frequency shift predicted by Baus's microscopic theory. The authors conclude that the temperature-dependent broadening and shifting of the plasma made at weak coupling is controlled primarily bymore » ionic interdiffusion transport.« less