Introduction

Dynamic processes in atomic liquids are nowadays well understood in terms of kinetic theory and computer calculations. Transport coefficients and dynamic scattering functions of liquid argon, for example, are well reflected by kinetic theories and equilibrium (MD) as well as nonequilibrium molecular dynamics (NEMD) calculations using Lennard–Jones (LJ) pair potentials.

The situation for molecular liquids like carbon dioxide, benzene or cyclohexane, is not so satisfactory. Kinetic theories are practically lacking, and few MD studies have been performed. Nonetheless, during the last ten years our understanding of the dynamics in molecular liquids has been considerably improved by equilibrium MD, as shown in Section 9.2.

Section 9.3 reviews briefly the computer simulation of liquids by NEMD and outlines how the viscosity and thermal conductivity may be evaluated. Two examples, which demonstrate how NEMD algorithms are tools to understand transport phenomena better, are given: (i) a calculation of the non–Newtonian viscosity of a simple liquid, and (ii) the density dependence of the contribution to the thermal conductivity from internal degrees of freedom.

Equilibrium molecular dynamics

Atomic liquids

The equilibrium molecular dynamics method

Given a system of N interacting particles treatable by classical statistical mechanics, the N–particle trajectory may be computed by solving numerically the equations of motion.

Molecular dynamics computations for a system of N(= 108) hard spheres were first performed by Alder and co–workers.