On the mode-coupling theory of vibrational line broadening in near-critical fluids

Dynamics of fluids near the consolute critical point: A molecular-dynamics study of the Widom–Rowlinson mixture

Molecular-dynamics simulations are presented for the dynamic behavior of the Widom-Rowlinson mixture [B. Widom, and J. S. Rowlinson, J. Chem. Phys. 52, 1670 (1970)] at its critical point. This model consists of two components where like species do not interact and unlike species interact via a hard-core potential. Critical exponents are obtained from a finite-size scaling analysis. The self-diffusion coefficient shows no anomalous behavior near the critical point. The shear viscosity and thermal conductivity show no divergent behavior for the system sizes considered, although there is a significant critical enhancement. The mutual diffusion coefficient, D(AB), vanishes as D(AB) approximately xi(-1.26 +/- 0.08), where xi is the correlation length. This is different from the renormalization-group (D(AB) approximately xi(-1.065)) mode coupling theory (D(AB) approximately xi(-1)) predictions. The theories and simulations can be reconciled if we assume that logarithmic corrections to scaling are important.

A Mode-Coupling Theory of Vibrational Line Broadening in Near-Critical Fluids

We present a fully microscopic mode-coupling theory of near-critical line broadening. All the structural and dynamical input required by the theory is calculated directly from intermolecular potentials. We compute vibrational frequency time-correlation functions and line shapes as the critical point is approached along both the critical isochore and the liquid-gas coexistence curve. Theory is shown to be in good agreement with simulation.